Laser assembly with spectral beam combining

ABSTRACT

A laser assembly ( 1210 ) for generating an assembly output beam ( 1212 ) includes a laser subassembly ( 1216 ) that emits a plurality of spaced apart first laser beams ( 1220 A), a plurality of spaced apart second laser beams ( 1220 B), a transform lens assembly ( 1244 ), a wavelength selective beam combiner ( 1246 ), and a path length adjuster ( 1299 ). The transform lens assembly ( 1244 ) collimates and directs the laser beams ( 1220 A) ( 1220 B) to spatially overlap at a focal plane of the transform lens assembly ( 1244 ). The path length adjuster ( 1299 ) is positioned in a path of the first laser beams ( 1220 A), the path length adjuster ( 1299 ) being adjustable to adjust of a path length the first laser beams ( 1220 A) relative to the second laser beams ( 1220 B).

RELATED APPLICATION

This application is a continuation in part of U.S. patent applicationSer. No. 16/242,921 filed on Jan. 8, 2019, and entitled “LASER ASSEMBLYWITH SPECTRAL BEAM COMBINING”. U.S. patent application Ser. No.16/242,921 claims priority on U.S. Provisional Application No.62/615,244 filed on Jan. 9, 2018, and entitled “LASER ASSEMBLY WITHSPECTRAL BEAM COMBINING”. As far as permitted, the contents of U.S.patent application Ser. No. 16/242,921 and U.S. Provisional ApplicationNo. 62/615,244 are incorporated herein.

BACKGROUND

Mid Infrared (“MIR”) laser assemblies that produce a MIR wavelengthoutput beam can be used in many fields such as, in medical diagnostics,pollution monitoring, leak detection, analytical instruments, homelandsecurity, remote chemical sensing, and industrial process control.Recently, lasers have been used to protect aircraft from sophisticatedheat-seeking missiles. Manufacturers are always searching for ways toimprove efficiency, beam quality, and power output of these laserassemblies.

SUMMARY

One embodiment is directed to a laser assembly that generates anassembly output beam. The laser assembly can include a lasersubassembly, a transform lens assembly, a wavelength selective beamcombiner, and a path length adjuster. The laser subassembly includes (i)a first laser module emits a plurality of spaced apart, substantiallyparallel first laser beams, and (ii) a second laser module that emits aplurality of spaced apart, substantially parallel second laser beams.The transform lens assembly is positioned in a path of the laser beams,the transform lens assembly collimating the laser beams and directingthe laser beams to spatially overlap at a focal plane of the transformlens. The wavelength selective beam combiner is positioned at the focalplane that combines the lasers beams to provide a combination beam thatis directed along a combination axis. The path length adjuster ispositioned in a path of the first laser beams, the path length adjusterbeing adjustable to adjust of a path length the first laser beamsrelative to the second laser beams.

As provided herein, the path length adjuster allows for a relativelylarge spectral gap between the first laser beams and the second laserbeams while still generating the multi-spectral assembly output beam.

The first laser module is spaced apart from the second laser module anemitter separation distance along an emitter array axis. In oneembodiment, the emitter separation distance is at least 0.5 millimeters.

The laser assembly can include a polarization rotator, wherein the laserbeams from the laser subassembly have a first polarization orientation,and the polarization rotator rotates the polarization so that the laserbeams directed at the beam combiner will have a second polarizationorientation that is ninety degrees different from the first polarizationorientation.

Additionally, the laser assembly can include a beam adjuster positionedin a path of the laser beams, the beam adjuster adjusting the spacingbetween the plurality of laser beams.

In one embodiment, the path length adjuster is positioned between thefirst laser module and the beam adjuster.

In another embodiment, the path length adjuster is positioned betweenthe beam adjuster and the beam combiner.

In still another embodiment, the path length adjuster is positionedbetween the first laser module and the transform lens assembly.

The laser assembly can also include an output coupler positioned on thecombination axis that redirects at least a portion of the combinationbeam back to the beam combiner as a redirected beam, and transmits aportion of the combination beam as the assembly output beam.

Further, the laser assembly can include a spatial filter positionedbetween the beam combiner and the output coupler that suppressescross-talk.

In one embodiment, the laser assembly includes: (i) an emitter body thatincludes a plurality of spaced apart emitters that cooperate to emit atleast a portion of the assembly output beam; (ii) a controller thatdirects current to the emitter body; and (iii) a laser mount that iselectrically connected the emitter body. The laser mount includes amounting region and a first gap region. The emitter body is coupled tothe laser mount with at least a portion of emitter body cantileveringover the first gap region. This inhibits shorting of the emitter array.

The laser mount can include a second gap region that is spaced apartfrom the first gap region, and the emitter body can cantilever over boththe first gap region and the second gap region. For example, at leastone emitter can be positioned over the first gap region and/or at leastone emitter can be positioned over the second gap region.

In another embodiment, the laser assembly includes: (i) a lasersubassembly including a first laser module that includes a plurality offirst emitters that emit a plurality of spaced apart, substantiallyparallel first laser beams, and a second laser module that includes aplurality of second emitters that emit a plurality of spaced apart,substantially parallel second laser beams; (ii) a transform lenspositioned in a path of the laser beams, the transform lens collimatingthe laser beams and directing the laser beams to spatially overlap at afocal plane of the transform lens; and (iii) a wavelength selective beamcombiner positioned at the focal plane that combines the lasers beams toprovide a combination beam that is directed along a combination axis.

In one embodiment, the transform lens includes a first lens segmenthaving a first focal length and a second lens segment having a secondfocal length that is different from the first focal length. The firstlens segment directs the first laser beams at the focal plane and thesecond lens segment directs the second laser beams at the focal plane.

The first lens segment and the second lens segment can be securedtogether. Further, the first lens segment and the second lens segmentcan be aligned along a lens axis.

In another embodiment, the laser assembly includes a laser subassembly,a beam adjuster, a transform lens, a wavelength selective beam combiner,and an output coupler. The laser subassembly emits a plurality of spacedapart, substantially parallel laser beams. The beam adjuster ispositioned in a path of the laser beams, and the beam adjuster canadjust the spacing between the plurality of laser beams. The transformlens is positioned in a path of the laser beams, and the transform lenscollimates the laser beams and directs the laser beams to spatiallyoverlap at a focal plane of the transform lens. The wavelength selectivebeam combiner is positioned at said focal plane, and the beam combinercombines the lasers beams to provide a combination beam that is directedalong a combination axis. Further, the output coupler is positioned onthe combination axis, and the output coupler redirects at least aportion of the combination beam back to the beam combiner as aredirected beam, and transmits a portion of the combination beam as theassembly output beam. Moreover, the laser subassembly can include aplurality of emitters, with each emitter generating a separate laserbeam.

As discussed in detail below, the beam adjuster can compress the spacingbetween the laser beams that propagate from the laser subassembly to thetransform lens. For example, in alternative, non-exclusive embodiments,the beam adjuster can reduce the spacing between the plurality of laserbeams by at least one quarter, one-half, two, three, four, five, six,seven, eight, nine, or ten times for laser beams propagating from thelaser subassembly towards the transform lens. As a result thereof, moreemitters can be used in the laser subassembly for a given configurationof the laser assembly, a spatial width of the assembly output beam isless, and/or the size of the configuration of the laser assembly can bereduced.

Further, in certain embodiments, the beam adjuster can be tuned (i) toselectively adjust the spacing between the plurality of laser beams thatpropagate from the laser subassembly towards the transform lens, (ii)selectively adjust a spectral width of the assembly output beam, (iii)selectively adjust the wavenumbers of the multi-spectral assembly outputbeam, and (iv) improve laser beam overlap with peak of gaindistribution.

Additionally, the laser assembly can include a polarization rotator thatrotates a polarization of the laser beams that are directed at the beamcombiner from the laser subassembly. In one embodiment, the laser beamsfrom the laser subassembly have a first linear polarization orientation,and the polarization of these laser beams is rotated by ninety degreesso that the laser beams directed at the beam combiner have a secondlinear polarization orientation that is orthogonal to the firstorientation. For example, the first polarization orientation can beperpendicular to an array axis of the emitters, and the secondorientation is parallel to an emitter array axis of the emitters. Incertain embodiments, the wavelength selective beam combiner is anoptical diffraction grating) that is more efficient for laser beamshaving a second polarization orientation.

As provided herein, each of the plurality of laser beams generated bythe laser subassembly has a different center wavenumber, and theassembly output beam is multi-spectral. Further, each of the pluralityof laser beams can have a different center wavenumber that is in theinfrared range. Alternatively, one or more of the laser beams can have adifferent center wavenumber that is outside the infrared range.

In certain embodiments, the laser assembly can also include a spatialfilter positioned between the beam combiner and the output coupler tosuppress optical cross-talk.

In one non-exclusive embodiment, the laser subassembly includes at leastsix separate emitters that cooperate to generate at least six, spacedapart, substantially parallel laser beams, with each of the separatelaser beams having a different center wavenumber.

In another embodiment, the laser subassembly includes a plurality ofseparate emitters, with each emitter generating one of the laser beams,with each of the laser beams having a different center wavenumber. Inthis embodiment, the laser assembly can include a system controller thatdirects current individually to each of the emitters.

In yet another embodiment, the laser assembly comprises: (i) a lasersubassembly that emits a first laser beam having a first centerwavenumber, and a second laser beam that is substantially parallel toand spaced apart a first beam separation distance from the first laserbeam, the second laser beam having a second center wavenumber that isdifferent from the first center wavenumber; (ii) a beam adjusterpositioned in a path of the laser beams, the beam adjuster adjusting thelaser beams so that the first laser beam is substantially parallel toand spaced apart from the second laser beam a first adjusted separationdistance that is different from the first beam separation distance;(iii) a transform lens that directs the laser beams adjusted by the beamadjuster to spatially overlap at a focal plane of the transform lens;(iv) a wavelength selective beam combiner positioned at the focal planethat combines the lasers beams to provide a combination beam that isdirected along a combination axis; and (v) an output coupler positionedon the combination axis that redirects at least a portion of thecombination beam back to the beam combiner as a multi-spectralredirected beam, and transmits a portion of the combination beam as themulti-spectral assembly output beam.

In this embodiment, the first laser beam from the transform lensimpinges on the beam combiner at a first beam angle, and the second beamfrom the transform lens impinges on the beam combiner at a second beamangle that is different than the first beam angle. With this design, thecombination beam is made up of a plurality of beams exiting from thebeam combiner that are substantially coaxial.

In still another embodiment, the laser assembly includes (i) a lasersubassembly that emits a plurality of spaced apart, substantiallyparallel laser beams; (ii) a transform lens positioned in a path of thelaser beams, the transform lens directs the laser beams to spatiallyoverlap at a focal plane of the transform lens; (iii) a wavelengthselective beam combiner positioned at the focal plane that combines thelasers beams to provide a combination beam that is directed along acombination axis; (iv) a polarization rotator that rotates apolarization of the laser beams that are directed at the beam combinerfrom the laser subassembly; and (v) an output coupler positioned on thecombination axis that redirects at least a portion of the combinationbeam back to the beam combiner as a redirected beam, and transmits aportion of the combination beam as the assembly output beam. In thisembodiment, the laser beams from the laser subassembly can have a firstpolarization orientation, and the laser beams directed at the beamcombiner from the transform lens can have a second polarizationorientation that is e.g., ninety degrees different from the firstorientation.

In another embodiment, the laser assembly includes (i) a lasersubassembly that emits a plurality of spaced apart, substantiallyparallel laser beams; (ii) a transform lens positioned in a path of thelaser beams, the transform lens directing the laser beams to spatiallyoverlap at a focal plane of the transform lens; (iii) a wavelengthselective beam combiner positioned at the focal plane that combines thelasers beams to provide a combination beam that is directed along acombination axis; and (iv) an output coupler positioned on thecombination axis that redirects at least a portion of the combinationbeam back to the beam combiner as a redirected beam, and transmits aportion of the combination beam as the assembly output beam; and (v) aspatial filter positioned between the beam combiner and the outputcoupler that suppresses cross-talk. In this embodiment, the spatialfilter can include a first spatial lens, a second spatial lens that isspaced apart from the first spatial lens, and a beam trimmer positionedbetween the spatial lenses.

In yet another embodiment, a method can include (i) emitting a pluralityof spaced apart, substantially parallel laser beams with a lasersubassembly; (ii) adjusting the spacing between the plurality of laserbeams with a beam adjuster positioned in a path of the laser beams;(iii) directing the laser beams adjusted by the beam adjuster tospatially overlap a focal plane with a transform lens positioned in apath of the laser beams from the beam adjuster; (iv) combining thelasers beams to provide a combination beam that is directed along acombination axis with a wavelength selective beam combiner positioned atthe focal plane of the transform lens; and (v) redirecting at least aportion of the combination beam back to the beam combiner as aredirected beam, and transmitting a portion of the combination beam asthe assembly output beam with an output coupler positioned on thecombination axis.

In another embodiment, the laser assembly includes (i) a lasersubassembly that emits a plurality of spaced apart, substantiallyparallel laser beams; (ii) a beam adjuster and a transform lenspositioned in a path of the laser beams, the transform lens directingthe laser beams to spatially overlap at a focal plane of the transformlens; (iii) a wavelength selective beam combiner positioned at the focalplane of the transform lens that combines the lasers beams to provide acombination beam that is directed along a combination axis; and (iv) anoutput coupler positioned on the combination axis that redirects atleast a portion of the combination beam back to the beam combiner as aredirected beam, and transmits a portion of the combination beam as theassembly output beam. In this embodiment, the beam adjuster can adjustan angle of incidence of each of the laser beams on the beam combiner.

In still another embodiment, a method includes (i) emitting a pluralityof spaced apart, substantially parallel laser beams with a lasersubassembly; (ii) directing the laser beams to spatially overlap at afocal plane with a transform lens; (iii) rotating the polarization ofthe laser beams that are directed at said focal plane; (iv) combiningthe lasers beams to provide a combination beam that is directed along acombination axis with a wavelength selective beam combiner positioned atsaid focal plane; and (v) redirecting at least a portion of thecombination beam back to the beam combiner as a redirected beam, andtransmitting a portion of the combination beam as the assembly outputbeam with an output coupler positioned on the combination axis.

In another embodiment, a method includes (i) emitting a plurality ofspaced apart, substantially parallel laser beams with a lasersubassembly; (ii) directing the laser beams to spatially overlap at afocal plane with a transform lens; (iii) combining the lasers beams toprovide a combination beam that is directed along a combination axiswith a wavelength selective beam combiner positioned at said focalplane; (iv) redirecting at least a portion of the combination beam backto the beam combiner as a redirected beam, and transmitting a portion ofthe combination beam as the assembly output beam with an output couplerpositioned on the combination axis; and (v) positioning a spatial filterbetween the beam combiner and the output coupler that suppressescross-talk.

The laser subassembly can include a first laser module having aplurality of first emitters, and a second laser module having aplurality of second emitters. Further, the first laser module can bespaced apart from the second laser module, with the first emitters andthe second emitters aligned along an emitter array axis.

In another embodiment, the laser assembly includes: (i) a lasersubassembly that emits a plurality of spaced apart, substantiallyparallel laser beams, (ii) a transform lens positioned in a path of thelaser beams, the transform lens collimating the laser beams anddirecting the laser beams to spatially overlap at a focal plane of thetransform lens; (iii) a wavelength selective beam combiner positioned atsaid focal plane that combines the lasers beams to provide a combinationbeam that is directed along a combination axis; and (iv) an outputcoupler positioned on the combination axis that redirects at least aportion of the combination beam back to the beam combiner as aredirected beam, and transmits a portion of the combination beam as theassembly output beam. The laser subassembly can include a first lasermodule having a plurality of first emitters, and a second laser modulehaving a plurality of second emitters. The first laser module is spacedapart from the second laser module, and the first emitters and thesecond emitters are aligned along an emitter array axis.

For example, the first emitters of the first laser module can be spacedapart from the second emitters of the second laser module an emitterseparation distance along the emitter array axis that is at least 0.5millimeters, and each laser module includes a laser mount.

Additionally, the laser assembly can include a polarization rotator. Forexample, the laser beams from the laser subassembly have a firstpolarization orientation, and the polarization rotator rotates thepolarization so that the laser beams directed at the beam combiner willhave a second polarization orientation that is, e.g., ninety degreesdifferent from the first orientation.

The laser assembly can include a beam adjuster positioned in a path ofthe laser beams, the beam adjuster adjusting the spacing between theplurality of laser beams.

The laser assembly can include a spatial filter positioned between thebeam combiner and the output coupler that suppresses cross-talk.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of this invention, as well as the invention itself,both as to its structure and its operation, will be best understood fromthe accompanying drawings, taken in conjunction with the accompanyingdescription, in which similar reference characters refer to similarparts, and in which:

FIG. 1A is a simplified illustration of an embodiment of a laserassembly;

FIG. 1B is a simplified illustration of a portion of the laser assemblyof FIG. 1A;

FIG. 1C is a simplified schematic illustrating features of the presentinvention;

FIG. 1D is a simplified illustration of a first set of different centerwavenumbers versus power generated by the laser assembly of FIG. 1A;

FIG. 1E is a simplified illustration of the first set of differentcenter wavenumbers versus angle of incidence on a beam combiner;

FIG. 1F is a simplified illustration of a second set of different centerwavenumbers versus power generated by the laser assembly of FIG. 1A;

FIG. 1G is a simplified illustration of the second set of differentcenter wavenumbers versus angle of incidence on the beam combiner;

FIG. 1H is a simplified illustration of a third set of different centerwavenumbers versus power generated by the laser assembly of FIG. 1A;

FIG. 1I is a simplified illustration of the third set of differentcenter wavenumbers versus angle of incidence on the beam combiner;

FIG. 2 is a simplified illustration of another embodiment of a laserassembly;

FIG. 3 is a simplified illustration of still another embodiment of alaser assembly;

FIG. 4 is a simplified illustration of yet another embodiment of a laserassembly;

FIG. 5 is a simplified illustration of another embodiment of the laserassembly;

FIG. 6 is a simplified illustration of yet another embodiment of a laserassembly;

FIG. 7 is a simplified illustration of still another embodiment of alaser assembly;

FIG. 8A is a simplified illustration of another embodiment of a laserassembly;

FIG. 8B is a simplified illustration of a first set of different centerwavenumbers versus power generated by the laser assembly of FIG. 8A;

FIG. 8C is a simplified illustration of another set of different centerwavenumbers versus power generated by the laser assembly of FIG. 8A;

FIG. 9 is a simplified illustration of still another embodiment of alaser assembly;

FIG. 10 is a simplified illustration of another embodiment of apolarization rotator;

FIG. 11 is a simplified illustration of another embodiment of awavelength selective beam adjuster;

FIG. 12 is a simplified illustration of yet another embodiment of alaser assembly;

FIG. 13 is a simplified illustration of still another embodiment of alaser assembly;

FIG. 14A is a simplified illustration of another embodiment of a laserassembly;

FIGS. 14B and 14C are alternative embodiments of a transform lensassembly;

FIG. 15A is a perspective illustration of a portion of a laser assemblyand a laser mount;

FIG. 15B is a side illustration of a portion of FIG. 15A;

FIG. 16A is a perspective illustration of a portion of another laserassembly and a laser mount; and

FIG. 16B is a side illustration of a portion of FIG. 16A.

DESCRIPTION

FIG. 1A is simplified top illustration of a first embodiment of a laserassembly 10 that generates an assembly output beam 12 (illustrated withan arrow). In certain embodiments, the laser assembly 10 includes alaser frame 14, a laser subassembly 16 that includes a plurality ofemitters 18 that cooperate to generate a plurality of laser beams 20(illustrated as arrows), a wavelength selective beam combinersubassembly 22 that transforms and combines the plurality of laser beams20 into the assembly output beam 12, and a system controller 24 thatcontrols the operation of the laser subassembly 16. In this embodiment,each of the laser beams 20 can be coherent. Additionally, the laserassembly 10 can include a power supply 26 (e.g. a battery, theelectrical grid, or a generator) that provides electrical power to thecontrol system 24. Further, the laser assembly 10 can be secured to arigid mount 28 such as a test or experimental bench, a frame of avehicle or aircraft, or other rigid structure. Moreover, the rigid mount28 can be thermally isolated. The design of each of the components ofthe laser assembly 10 can be varied to vary the characteristics of theassembly output beam 12.

As an overview, in certain embodiments, the laser assembly 10 is acompact, high efficiency, high output, external cavity laser assembly 10that spectrally combines the laser beams 20 of multiple individualemitters 18 into a single spatial, multi-spectral, output beam 12 thatis diffraction-limited or near diffraction-limited. As a result thereof,multiple emitters 18, each generating a laser beam 20 having relativelymoderate output power, can be combined into a multi-Watt moduleconfiguration that offers many practical benefits. For example, a lowerper-facet intensity of each emitter 18 translates into lower thermalstress on the individual emitters 18, providing much longer term systemreliability. In addition, emitters 18 with lower power requirements canbe manufactured with much higher yields, providing a dependable supplyat lower costs. Further, the combined beams provide more power whilepreserving good spatial quality.

Moreover, the optical power of the assembly output beam 12 can bechanged by changing the number of emitters 18 used in the lasersubassembly 14. Thus, the design of laser assembly 10 can be easilyadjusted to add or remove emitters 18 based on the desired output powerof the assembly output beam 12. As a non-exclusive example, the laserassembly 10 can be designed so that the assembly output beam 12 has anoptical power of between five to fifty watts. Stated in another fashion,in alternative, non-exclusive embodiments, the laser assembly 10 can bedesigned so that the assembly output beam 12 has an optical power of atleast five, ten, fifteen, twenty, twenty-five, thirty, thirty-five,forty, forty-five, or fifty watts. However, optical powers of less thanfive, or greater than fifty watts are possible.

As provided herein, the resulting assembly output beam 12 is made up ofthe plurality of individual laser beams 20 that are collimated anddirected by the beam combiner subassembly 22 to co-propagate, and becoaxial with each other along an output axis 12A. As used herein, theterm “combines” as used in regards to the assembly output beam 12 shallmean (i) that the beams are directed substantially parallel to oneanother (i.e, the beams travel along substantially parallel axes), and(ii) that the beams are fully or partly spatially overlapping.

Further, as provided herein, the assembly output beam 12 will bemultispectral because each of the individual emitters 18 is lasing at adifferent center wavenumber as a result of the arrangement of the laserassembly 10. In certain embodiments, the laser assembly 10 is designedso that the assembly output beam 12 has a relatively small spectralwidth. In alternative, non-exclusive embodiments, the laser assembly 10is designed so that the assembly output beam 12 has a spectral width ofless than 0.025, 0.05, 0.1, 0.2, 0.3, 0.5, 0.75, 1, or 1.5 microns. Forexample, a ten emitter 18 design could achieve a spectral width of lessthan 0.1 microns, while a twenty emitter 18 design could achieve aspectral width of less than 0.2 microns.

The designs described herein provide the following benefits: (i) gettingmore power into the output beam 12 while preserving good spatialquality; (ii) getting high power out of the laser assembly 10 with arelatively small footprint; and/or (iii) providing different frequencypulses of light that travel down the same output axis 12A (at the sametime or at different times depending on how the emitters 18 arecontrolled).

A number of Figures include an orientation system that illustrates an Xaxis, a Y axis that is orthogonal to the X axis and a Z axis that isorthogonal to the X and Y axes. It should be noted that these axes canalso be referred to as the first, second and third axes.

The laser frame 14 is rigid, thermally stable, supports the othercomponents of the laser assembly 10, and maintains the precise alignmentof the components of the laser assembly 10. In FIG. 1, for simplicity,the laser frame 14 is illustrated as a flat plate. However, for example,the laser frame 14 can be a sealed or unsealed housing that encirclesand provides a controlled environment for the other components of thelaser assembly 10. If the laser frame 14 is a housing, the laser frame14 can include a window (not shown) for the assembly output beam 12 toexit the laser frame 14. Further, if the laser frame 14 is sealed, itcan be filled with an inert gas, or another type of fluid, or the sealedchamber can be subjected to a vacuum. Still alternatively, for example,desiccant or another drying agent can be positioned in the laser frame14 to trap gases that could absorb laser emissions, cause corrosion,and/or to cause condensation.

In one, non-exclusive embodiment, the laser subassembly 16 includes acommon laser mount 30, the plurality of emitters 18, and a lens array 32that cooperate to generate the array of laser beams 20.

The laser mount 30 retains and secures the emitters 18 to the laserframe 14. In one embodiment, the laser mount 30 includes a mounting base30A and a thermally conductive sub-mount 30B. In one non-exclusiveembodiment, the mounting base 30A is rigid, generally rectangularshaped, and includes a plurality of embedded base passageways 30C, e.g.micro-channels (only a portion is illustrated in phantom) that allow forthe circulation of a circulation fluid (not shown) through the mountingbase 30A. Non-exclusive examples of suitable materials for the mountingbase 30A include copper, Glidcop, MolyCopper, molybedium, coppertungsten (CuW), aluminum, and aluminum nitride (ALN).

The sub-mount 30B retains the multiple emitters 18 and secures theemitters 18 to the mounting base 30A. In one embodiment, the sub-mount30B is rectangular plate shaped and is made of rigid material that has arelatively high thermal conductivity to act as a conductive heatspreader. In one non-exclusive embodiment, the sub-mount 30B has athermal conductivity of at least approximately 170 watts/meter K. Withthis design, in addition to rigidly supporting the emitters 18, thesub-mount 30B also readily transfers heat away from the emitters 18 tothe mounting base 30A. For example, the sub-mount 30B can be fabricatedfrom a single, integral piece of copper, copper-tungsten (CuW),copper-moly, molybdenium, aluminum-nitride (AlN), beryllium oxide (BeO),diamond, silicon carbide (SiC), or other material having a sufficientlyhigh thermal conductivity.

In certain embodiments, the material used for the sub-mount 30B can beselected so that its coefficient of thermal expansion matches thecoefficient of thermal expansion of the emitters 18.

Additionally, the laser assembly 10 can include a thermal controller 34that controls the temperature of the mounting base 30A and/or theemitters 18. For example, the thermal controller 34 can include (i) oneor more pumps (not shown), chillers (not shown), heaters (not shown),and/or reservoirs that cooperate to circulate a hot or cold circulationfluid (not shown) through the base passageways 30C to control thetemperature of the mounting base 30A, and (ii) a temperature sensor 34A(e.g., a thermistor) that provides feedback for closed loop control ofthe temperature of the mounting base 30A and/or the emitters 18. Withthis design, the thermal controller 34 can be used to directly controlthe temperature of the mounting base 30A at a predetermined temperature.

With this design, the thermal controller 34 can be used to maintainnear-constant temperature of the laser assembly 10 for purposes ofmaintaining optical alignment over (i) a range of environmentaltemperatures; (ii) a range of heat loads produced when powering theemitters 18; and/or (iii) a range of heat loads generated within theoptical elements due to absorption, scattering, and stray light.

In the non-exclusive embodiment illustrated in FIG. 1A, the thermalcontroller 34 is positioned outside the laser frame 14 and thetemperature sensor 34A is positioned on the mounting base 30A.Alternatively, the thermal controller 34 can be in direct thermalcontact with the mounting base 30A and/or positioned on or in the laserframe 14. Additionally, or alternatively, the thermal controller 34 canalso include one or more cooling fans and/or vents to further remove theheat generated by the operation of the laser assembly 10. Further, thetemperature sensor 34A can be placed in the coolant path, though otherpositions will also work.

The number, size, shape and design of the emitters 18 can be varied toachieve the desired characteristics of the assembly output beam 12. Forexample, the laser assembly 16 can include between two and fiftyemitters 18 that are arranged in an emitter array. In FIG. 1A, the laserassembly 10 includes six separate, spaced apart emitters 18. Asalternative, non-exclusive examples, the laser assembly 16 can includeat least 4, 5, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40 or 50 separateemitters 18 that are arranged in the linear emitter array.

Additionally, in alternative, non-exclusive embodiments, each emitter 18can be designed and powered to generate at least approximately 0.5,0.75, 1, 1.25, 1.5, or 2 watts of output power. However, other outputpowers are possible.

As non-exclusive examples, each of the emitters 18 can be a QuantumCascade (“QC”) gain medium, a laser diode (e.g. Gallium Antimony), or aninterband cascade laser. Further, in one, non-exclusive embodiment, eachemitter 18 is an infrared laser source that directly generates a laserbeam 20 having a center wavelength that is in the mid to far infraredwavelength range of three to thirty microns. In another non-exclusiveembodiment, each emitter 18 is a mid-infrared laser source that directlygenerates a laser beam 20 having a center wavelength that is in themid-infrared wavelength range of two to twenty microns.

The density and spacing of the emitters 18 can be selected based on theability to remove the heat with the thermal controller 34.

In certain embodiments, the emitters 18 can be bonded/mounted epi-sidedown to the sub-mount 30B to allow for (i) individually addressabilityof emitters 18; (ii) high duty factor optimization; (iii) high capacityliquid cooling of the emitters via the mounting base 30A; and/or (iv)maximum optical power while minimizing core/gain layer and facet opticaltemperature. For example, if each emitter 18 is a QC gain medium, eachemitter 18 can be hard-soldered or soft-soldered to the sub-mount 30Bdirectly with thin, highly-conductive solder such as Indium.

If the emitters 18 are individually addressable, (i) the laser assembly10 will still be operational in the event of failure of one emitter or asubset of the emitters 18; and (ii) the emitters 18 can be powered on oroff individually by the system controller 24. Alternatively, theemitters 18 can be electrically connected such that all of the emitters18 are powered on or off concurrently. In contrast, if each individualemitter 18 is sequentially powered, the center wavelength (wavenumber)of the assembly output beam 12 will change as each individual emitter 18is powered because each emitter 18 will lase at a different centerwavenumber as detailed below. This allows for discretized form ofspectroscopy whereby light of distinct wavenumbers can be generatedindependently by the distinct emitters 18 and directed at an analyte(not shown). Spectral signatures of the analyte (e.g., absorption,reflection, birefringence, etc) may be correlated to the distinctwavenumbers via e.g., time-division multiplexing i.e., encoding theemission time of each individual emitter to the detector signal. Manyother schemes of encoding are possible and well known to those skilledin the art of spectroscopy. Further, the emitters may be turned on andoff in subsets rather than individually to exploit possible furtherimprovements in signal detection efficiency.

FIG. 1B is an enlarged view of the emitters 18, the lens array 32, andthe beam adjuster 42 of the beam combiner 22 of FIG. 1A. In thisembodiment, (i) the emitters 18 are aligned and spaced apart along aone-dimensional emitter axis 35A, (ii) the emitters 18 are centered onan emitter central axis 35B, and (iii) each emitter 18 generates one ofthe laser beams 20. For ease of discussion, moving top to bottom, theemitters 18 can be labeled (i) a first emitter 18A that emits a firstlaser beam 20A along a first beam axis 36A; (ii) a second emitter 18Bthat emits a second laser beam 20B along a second beam axis 36B; (iii) athird emitter 18C that emits a third laser beam 20C along a third beamaxis 36C; (iv) a fourth emitter 18D that emits a fourth laser beam 20Dalong a fourth beam axis 36D; (v) a fifth emitter 18E that emits a fifthlaser beam 20E along a fifth beam axis 36E; and (vi) a sixth emitter 18Fthat emits a sixth laser beam 20F along a sixth beam axis 36F. It shouldbe noted that any of the emitters 18 can be referred to as the first,second, third, etc emitter 18. Somewhat similarly, any of the laserbeams 20 can be referred to as a first, second, third, etc. laser beam20.

In one embodiment, each emitter 18 has a back facet 18G and an opposedfront facet 18H that faces the lens array 32, and each emitter 18 isdesigned to only emit from the front facet 18H. In this embodiment, theback facet 18G is coated with a high reflectivity dielectric ormetal/dielectric coating to minimize optical losses from the back facet18G and to allow the back facet 18G of each emitter 18 to function afirst laser cavity end of a cavity for each emitter 18. Further, thefront facet 18H can include an anti-reflective dielectric coating tominimize coupled cavity effects within the laser assembly 10. Forexample, the coating on the front facet 18H can be optimized to minimizereflectivity across the available gain-bandwidth of the emitters 18. Inone non-exclusive embodiment, the anti-reflective coating can have areflectivity of less than approximately two percent, and the highlyreflective coating can have a reflectivity of greater than ninetypercent.

With reference to FIGS. 1A and 1B, the wavelength selective beamcombiner subassembly 22 includes an output coupler 48 that functions asa common, second cavity end for each emitter 18. With this design, eachemitter 18 has a separate external cavity that is defined by the backfacet 18G of the respective emitter 18, and the common output coupler48. As a result thereof, each emitter 18 operates in a separate externalcavity independent from the other emitters 18.

Further, as explained in more detail below, the external cavity for eachemitter 18 is slightly different. Thus, each emitter 18 will lase at adifferent center wavenumber, even if the characteristics of each of theemitters 18 are identical. More specifically, the first laser beam 20A,the second laser beam 20B, the third laser beam 20C, the fourth laserbeam 20D, the fifth laser beam 20E, and the sixth laser beam 20F willeach lase at a different center wavenumber.

With reference to FIG. 1B, an emitter spacing 35C between adjacentemitters 18 aligned along the one dimensional, emitter axis 35A can bevaried based on the ability to remove the heat with the thermalcontroller 34 (illustrated in FIG. 1A). As alternative, non-exclusiveexamples, the emitter spacing 35C can be less than approximately 0.1,0.2, 0.3, 0.4, 0.5, 0.75, 1, 1.5, 2, 2.5, or 3 millimeters. Stated inanother fashion, the emitter spacing 35C can be between approximately0.1 and 3 millimeters.

Each of the laser beams 20 emitted from the emitters 18 is diverging andnot-collimated. The lens array 32 individually collimates the laserbeams 20 emitted from the emitters 18. In certain embodiments, (i) thelens array 32 includes a separate micro-lens for each emitter 18, (ii)the micro-lenses are aligned and spaced apart along a one-dimensionallens array axis 38A, and (iii) the lens array 32 has a lens central axis38B that is coaxial with the emitter central axis 35B. In certainembodiments, the lens array 32 has the same spacing (pitch) as theemitter array 18. In FIG. 1B, the micro-lenses are slightly spaced apart(and adjacent to each other) along the lens array axis 38A.Alternatively, the lens array 32 can be designed so that adjacentmicro-lenses are in contact with each other (no spacing therebetween).

For ease of discussion, moving top to bottom, the lenses of the lensarray 32 can labeled (i) a first lens 32A that is coaxial with the firstbeam axis 36A and that collimates the first laser beam 20A; (ii) asecond lens 32B that is coaxial with the second beam axis 36B and thatcollimates the second laser beam 20B; (iii) a third lens 32C that iscoaxial with the third beam axis 36C and that collimates the third laserbeam 20C; (iv) a fourth lens 32D that is coaxial with the fourth beamaxis 36D and that collimates the fourth laser beam 20D; (v) a fifth lens32E that is coaxial with the fifth beam axis 36E and that collimates thefifth laser beam 20E; and (vi) a sixth lens 32F that is coaxial with thesixth beam axis 36F and that collimates the sixth laser beam 20F. Any ofthe lenses can be referred to as the first, second, third, etc lens.

In one, non-exclusive embodiment, each lens 32A-32F is a spherical lenshaving an optical axis that is aligned and coaxial with the respectivebeam axis 36A-36F. In one, non-exclusive embodiment, each lens 32A-32Fhas a diameter of between approximately 50 microns and 3 millimeters.Further, in one, non-exclusive embodiment, each lens 32A-32F is spacedapart from the respective emitter 18A-18F a working distance of betweenapproximately 10 microns and 500 microns.

The lens array 32 creates diffraction limited or near diffractionlimited laser beams 20A-20F. As non-exclusive examples, each of the lens32A-32F can (i) be aspheric; (ii) be conic; (iii) be spherical; (iv) bePlano-Convex, Bi-convex, a Meniscus lens, or double sided; (v) betransparent in lasing optical bandwidth of the laser beams 20A-20F; (vi)be anti-reflective coated on both sides; (vii) be fabricated usinggreyscale lithographically fabrication; (viii) be micro-machined usingdiamond turning; (ix) be molded; (x) be made of a low distortionsubstrate; (xi) dissipate heat and prevent thermal runaway at highpower; (xii) have low insertion loss; (xiii) be spaced to match emitterspacing; (xiv) include metallization to allow soldering to reduceoutgassing materials and to provide conductive heat path.

In one embodiment, each of the lenses 32A-32F can have a high numericalaperture (e.g. 0.75 or greater) and can be designed to match the outputfrom the respective emitter 18A-18F to maximize collection efficiency.Stated in another fashion, the type of material used for each lens32A-32F can be varied to match the wavelengths of the laser beams20A-20F. For example, for infrared emitters 18A-18F, each lens 32A-32Fcan comprise materials selected from the group of germanium, silicon,sapphire, or ZnSe. However, other materials may also be utilized thatare effective with the wavelengths of the beams 32A-32F.

Moreover, in certain embodiments, the lenses 32A-32F (i) can haveattachment points designed to maintain alignment after temperatureexcursions/cycles; (ii) can have a heat path to inhibit overheating andmisalignment due to thermal loading; (iii) can be bonded to acoefficient of thermal expansion matched lens frame (not shown) with athin adhesive bond line, and/or (iv) can be attached bythermally-conductive epoxy or solder to a metal lens frame.

In summary, the lens array 32 is aligned with the emitters 18 to producethe parallel laser beams 20A-20F having matching or nearly matchingdivergences. In this embodiment, (i) the center of the first laser beam20A is spaced apart from the center of the adjacent second laser beam20B a first beam separation distance 40A; (ii) the center of the secondlaser beam 20B is spaced apart from the center of the adjacent thirdlaser beam 20C a second beam separation distance 40B; (iii) the centerof the third laser beam 20C is spaced apart from the center of theadjacent fourth laser beam 20D a third beam separation distance 40C;(iv) the center of the fourth laser beam 20D is spaced apart from thecenter of the adjacent fifth laser beam 20E a fourth beam separationdistance 40D; and (iv) the center of the fifth laser beam 20E is spacedapart from the center of the adjacent sixth laser beam 20F a fifth beamseparation distance 40E. In one, non-exclusive embodiment, each beamseparation distance 40A-40E can be between 0.05 and 3 millimeters.Further each beam separation distance 40A-40E can be the same orslightly different.

As illustrated in FIG. 1B, the array of laser beams 20 have a combinedbeam profile 40F measured transverse to the emitter central axis 35B. Asa non-exclusive example, the laser subassembly 16 can be designed sothat the combined beam profile 40F is between approximately 0.5 and 100millimeters.

With reference back to FIG. 1A, the wavelength selective beam combinersubassembly 22 transforms and combines the array of laser beams 20 intothe assembly output beam 12. In this embodiment, the beam combinersubassembly 22 includes a beam adjuster 42, a transform lens assembly44, a wavelength selective beam combiner 46, and the output coupler 48.The design of each of these components can be varied to adjust thecharacteristics of the assembly output beam 12.

The beam adjuster 42 can be a beam compressor that adjusts the spacingbetween the laser beams 20 and adjusts the spectral width of theassembly output beam 12. Depending upon the direction in which the laserbeams are propagating, the beam adjuster 42 can spatially demagnify orspatially magnify the laser beams. In FIG. 1A, the beam adjuster 42 ispositioned in a path of the laser beams 20 from the laser subassembly 16between the lens array 32 and the transform lens assembly 44. In thisembodiment, for the laser beams 20 propagating left to right in FIG. 1A,the beam adjuster 42 is designed to converge and subsequently collimate(demagnify) the laser beams 20 to provide an array of adjusted laserbeams 50 that are more tightly packed. In this design, the individualbeams 20 leaving the microlens array 32 are slightly diverging. When thebeams leave the beam adjuster 42, the beams will be diverging amagnification factor times the divergence entering the beam adjuster 42.The magnification factor is the same as the factor they are spatiallycompressed by the beam adjuster 42. For example, for FIG. 1A, a 3 x beamadjuster 42 will result in a three times compression of the beams 20directed left to right, and a three times divergent for beams 20directed from right to left.

As provided herein, the specific center wavenumber of the laser beam 20generated by each emitter 18 is tied to an angle of incidence of itsrespective laser beam 20 on the wavelength selective beam combiner 46.Further, the angle of incidence of each laser beam 20 on the wavelengthselective beam combiner 46 is tied to the spacing of the laser beams 20at the transform lens assembly 44. With this design, when the beamadjuster 42 reduces the spacing between the laser beams 20, the beamadjuster 42 also reduces the range of angles of incidences on the beamcombiner 46, and thus reduces the spectral width of the assembly outputbeam 12.

With this design, the beam adjuster 42 can be used to increase thenumber of emitters 18 that can be used for a given form factor bycompressing the spacing between the beams 20, while still maintaining arelatively small spectral width. Stated in another fashion, the beamadjuster 42 allows for the use of a relatively large number ofadequately spaced apart emitters 18 for a relatively small form factor.Further, by compressing the spacing between the beams 20, a smallertransform lens assembly 44 can be used and/or the space between thetransform lens assembly 44 and the beam combiner 46 can be reduced. As aresult thereof, the size of the laser assembly 10 can be reduced.

Moreover, because the beam adjuster 42 compresses the spacing betweenthe beams 20, the spectral width of the assembly output beam 12 isreduced, and the wavelengths of the beams 20 from the emitters 18 arerelatively close and can fit under the spectral beam peak. This improvesthe efficiency of the laser assembly 10 and the output of the assemblyoutput beam 12.

Alternatively, for laser beams propagating from right to left in FIG.1A, the beam adjuster 42 diverges and subsequently collimates(magnifies) the laser beams 20. With this design, the beam adjuster 42expands the spacing between the laser beams moving right to left so thatthe laser beams 20 are properly spaced to be directed back to therespective emitters 18.

With reference to FIG. 1B, in one embodiment, the beam adjuster 42 is atwo lens system that functions somewhat similar to telescope thatreduces (demagnifies) the spacing between the laser beams propagatingleft to right in FIG. 1B, and expands (magnifies) the spacing(divergence) of the laser beams propagating right to left in FIG. 1B. Inthis embodiment, the beam adjuster 42 can include a first adjuster lens42A and a second adjuster lens 42B that are spaced apart along anadjuster central axis 42C that can be coaxial with the emitter centralaxis 35B and the lens central axis 38B. In this embodiment, the firstadjuster lens 42A is closer than the second adjuster lens 42B to theemitters 18.

Further, in this embodiment, the first adjuster lens 42A can be apositive lens, and the second adjuster lens 42B can be a negative lenswhich compresses the chief rays of the emitters spatially. Moreover, inthis embodiment, each of the beams 20 is transmitted through the commonfirst adjuster lens 42A concurrently and through the common secondadjuster lens 42B concurrently.

In one embodiment, the beam adjuster 42 can be somewhat similar indesign to a refracting telescope, such as a Galilean telescope or aKeplerian telescope.

For laser beams moving left to right, the first adjuster lens 42Acontracts and/or converges the spacing between the laser beams, and thesecond adjuster lens 42B subsequently re-directs the laser beams 20 tobe parallel again. Stated in another fashion, for the laser beams 20propagating left to right in FIG. 1B, the beam adjuster 42 demagnifiesthe laser beams 20 to provide an array of parallel, adjusted laser beams50 that are more tightly packed. Moving top to bottom, (i) the firstlaser beam 20A is transformed into the first adjusted laser beam 50A;(ii) the second laser beam 20B is transformed into the second adjustedlaser beam 50B; (iii) the third laser beam 20C is transformed into thethird adjusted laser beam 50C; (iv) the fourth laser beam 20D istransformed into the fourth adjusted laser beam 50D; (v) the fifth laserbeam 20E is transformed into the fifth adjusted laser beam 50E; and (vi)the sixth laser beam 20F is transformed into the sixth adjusted laserbeam 50F.

In this embodiment, (i) the center of the first adjusted laser beam 50Ais spaced apart from the center of the adjacent, second adjusted laserbeam 20B a first adjusted beam separation distance 52A; (ii) the centerof the second adjusted laser beam 50B is spaced apart from the center ofthe adjacent, third adjusted laser beam 50C a second adjusted beamseparation distance 52B; (iii) the center of the third adjusted laserbeam 50C is spaced apart from the center of the adjacent, fourthadjusted laser beam 50D a third adjusted beam separation distance 52C;(iv) the center of the fourth adjusted laser beam 50D is spaced apartfrom the center of the adjacent, fifth adjusted laser beam 50E a fourthadjusted beam separation distance 52D; and (iv) the center of the fifthadjusted laser beam 50E is spaced apart from the center of the adjacentsixth adjusted laser beam 50F a fifth adjusted beam separation distance52E.

In one, non-exclusive embodiment, each adjusted beam separation distance52A-52E can be between 0.03 and 3 millimeters. Further each adjustedbeam separation distance 52A-52E can be the same or slightly different.Moreover, in certain embodiments, each beam separation distance 40A-40Eis greater than each corresponding adjusted beam separation distance52A-52E. Moreover, as illustrated in FIG. 1B, the array of adjustedlaser beams 50 can have an adjusted, combined beam profile 52F measuredtransverse to the adjuster central axis 42C.

As a non-exclusive alternative embodiments, (i) for laser beamspropagating left to right, the beam adjuster 42 can reduce the spacingof the laser beams by a factor of between approximately 1.1 and ten; and(ii) for laser beams propagating right to left, the beam adjuster 42will increase the spacing of the laser beams by the same factor. Statedin another fashion, in certain non-exclusive alternative embodiments,(i) for laser beams moving left to right, the beam adjuster 42 canreduce the spacing of the laser beams by a factor of at least one andone-tenth, one and one-half, two, three, four, five, six, seven, eight,nine, or ten; and (ii) for laser beams moving right to left, the beamadjuster 42 can increase the spacing of the laser beams by the samefactor. Stated in yet another fashion, in alternative, non-exclusiveembodiments, the beam adjuster 42 can be designed so that each beamseparation distance 40A-40E is at least one and one-tenth, one andone-half, two, three, four, five, six, seven, eight, nine, or ten timegreater than each corresponding adjusted beam separation distance52A-52E. Stated in still another fashion, in alternative, non-exclusiveembodiments, the beam adjuster 42 can be designed so that the combinedbeam profile 40F is at least one and one-tenth, one and one-half, two,three, four, five, six, seven, eight, nine, or ten time greater than theadjusted, combined beam profile 52F.

Moreover, by compressing the beams, the beam adjuster 42 will adjust theangle of incidence of almost all of the beams onto the beam combiner 46.For example, an angle of incidence of a center beam may not be affectedby the beam adjuster 42, while the angle of incidence of the other beamswill be adjusted by the beam adjuster 42.

The lenses 42A, 42B can be optimized (i) for low loss, aberration, anddistortion; (ii) to preserve power efficiency in external cavity; (iii)for narrow or wide array width of the element array; (iv) for narrow orwide gain-bandwidth of the emitters 18; (v) for high beam quality;and/or (vi) for a field of view that matches the laser beams 20. In FIG.1B, the adjuster lenses 42A, 42B are transmissive. Alternatively, thebeam adjuster 42 can be designed to be comprised of reflective opticalelements or a combination of reflective and transmissive opticalelements.

Additionally, in one non-exclusive embodiment, the beam adjuster 42 caninclude a lens mover 42D (illustrated as a box) that moves one or bothof the adjuster lenses 42A, 42B to selectively adjust thecharacteristics (e.g. the demagnification) of the beam adjuster 42. Forexample, the lens mover 42D can include one or more actuators that arecontrolled by the system controller 24 (or manually) to selectivelyadjust the spacing between lenses 42A, 42B, along the adjuster centralaxis 42C. This will allow for variable magnification (zoom) to allow forselective adjustment of the spectral width of the assembly output beam12, and adjustment of the wavenumbers that make up the assembly outputbeam 12, while maintaining the spacing between the lens array 32 and thetransform lens assembly 44.

Generally speaking, as the demagnification is increased, (i) the spacingbetween adjacent adjusted laser beams 50 is decreased, (ii) the range ofangles of incidences of the laser beams 50 on the beam combiner 46 isdecreased, and (iii) the spectral width of the assembly output beam 12is decreased. Conversely, as the demagnification is decreased, (i) thespacing between adjacent adjusted laser beams 50 is increased, (ii)range of angles of incidences of the laser beams 50 on the beam combiner46 is increased, and (iii) the spectral width of the assembly outputbeam 12 is increased.

In certain embodiments, the wavelength selective beam adjuster 42 alsoreduces and suppresses optical crosstalk. This improves the efficiencyof each of the emitters 18.

With reference back to FIG. 1A, the transform lens assembly 44up-collimates the adjusted laser beams 50, and then directs andspatially overlaps the individual laser beams 50 onto a focal plane 54of the transform lens assembly 44, and the wavelength selective beamcombiner 46 is positioned at least partly at the focal plane 54. Thefocal plane 54 is perpendicular to the optical axis of the transformlens assembly 44 (e.g. the co-axis of the lens elements of the transformassembly). The transform lens assembly 44 includes at least onetransform lens 44A. The transform lens assembly 44 can be optimized (i)for high extraction/power efficiency; (ii) for narrow or wide arraywidth; (iii) for narrow or wide gain-bandwidth emitters; (iv) for highbeam quality; and/or (v) for a field of view that matches the adjustedlaser beams 50.

With the present design, each of the laser beams 50 will be incident onthe beam combiner 46 at a different angle of incidence (relative tonormal of the beam combiner 46). More specifically, with reference toFIG. 1C, (i) the first adjusted laser beam 50A will have a first angleof incidence 56A relative to normal 46A of the beam combiner 46(illustrated as a box); (ii) the second adjusted laser beam 50B willhave a second angle of incidence 56B relative to normal 46A of the beamcombiner 46 and the focal plane 54; (iii) the third adjusted laser beam50C will have a third angle of incidence 56C relative to normal 46A ofthe beam combiner 46; (iv) the fourth adjusted laser beam 50D will havea fourth angle of incidence 56D relative to normal 46A of the beamcombiner 46; (v) the fifth adjusted laser beam 50E will have a fifthangle of incidence 56E relative to normal 46A of the beam combiner 46;and (vi) the sixth adjusted laser beam 50E will have a sixth angle ofincidence 56E relative to normal 46A of the beam combiner 46. Further,each angle of incidence 56A-56F will be different.

It should be noted that with the design illustrated in FIGS. 1A and 10,each beam 50A-50F will exit the beam combiner 46 at substantially thesame angle relative to normal 46A.

In the external cavity arrangements disclosed herein, the design of thebeam combiner 46, and the angle of incidence 56A-56F of each laser beam50A-50F on the beam combiner 46 will dictate what wavelength willexperience the least loss per round trip in the external cavity and thusdominate the center wavenumber of the respective laser beam 50A-50F.Thus, the spectral width of the adjusted output beam 20, and theindividual center wavenumber each emitter 18 is lasing at, can beadjusted by adjusting the angle of incidences 56A-56F via the beamadjuster 42.

With reference to FIGS. 1A and 10, the beam combiner 46 combines thelaser beams 50A-50F into a multi-spectral, combination beam 58 that isdirected along a common combination axis 58A. In this embodiment, thecombination beam 58 is made up of the laser beams 50A-50F that aredirected by the beam combiner 54 to be coaxial. Further, the combinationbeam 58 has minimal degradation when compared to the original laserbeams 50A-50F. In certain embodiments, the beam quality of the combinedbeam is not greatly degraded over the beam quality of the individualbeams. In one specific embodiment, a M-squared value of the combinedbeam is not much larger than a M-squared value of the individual beams.For example, the M-squared value of the combined beam can be between1.1-1.2 and the M-squared value of each of the individual beams can bebetween 1.1-1.2.

In one embodiment, the wavelength selective beam combiner 46 is adispersive beam combiner such as a diffraction grating (i) having highdiffraction efficiency for a wide range of angles of incidences; (ii)that can handle forward and reverse propagating beams; (iii) that isdesigned for high power; (iv) that is photo-etched, ruled, replicated,gray scale, binary; (v) that has low scatter; (vi) that has a lowcoefficient of thermal expansion, (vii) that has high optical flatness,and/or (vii) that is optimized for the wavenumbers of the emitters 18.In FIG. 1A, the beam combiner 46 is a reflective diffraction gratingthat can be aluminum, silver, or gold coated. In this embodiment, thediffraction grating 46 is a plate that includes a large number of veryfine parallel grooves that have an inter-groove spacing referred to asthe grating period (“GP”).

Alternatively, the beam combiner 46 can be a transmission grating thatis transmissive to the wavelengths generated by the emitter 18 andcoated on both sides with appropriate anti-reflective coatings. Stillalternatively, the beam combiner 46 can be a single prism, ordiffractive optical element (DOE).

With reference back to FIG. 1A, the output coupler 48 is positioned onthe combination axis 58A and functions as the second defining boundaryof the external cavity for each emitter 18. In one embodiment, theoutput coupler 48 is an optical element that includes a first couplerside 48A that is coated with a partly reflective coating that isoptimized to maximize extraction efficiency for all emitters 18, and asecond coupler side 48B that is coated with an anti-reflective coating.With this design, the first coupler side 48A cooperates with the backfacet 18G of each emitter 18 to form an external cavity for each emitter18. Stated in another fashion, in this design, the first coupler side48A redirects at least a portion of the combination beam 58 back to thebeam combiner 46 as a multi-spectral redirected beam 60 (illustrated asa dashed line), and transmits a portion of the combination beam 46 asthe multi-spectral assembly output beam 12 along the output axis 12Athat is coaxial with the combination axis 58A in this embodiment.

In one non-exclusive embodiment, (i) the first coupler side 48A has areflectivity of between approximately one to thirty percent, (ii) theoutput coupler 48 has a high thermal conductivity; (iii) theanti-reflective coated second coupler side 48B reduce optical losses;and (iv) the output coupler 48 can be wedged to reduce feedback.

The fraction of the beam reflected by the output coupler 60 retraces thepath of 58 in reverse, the beam combiner 46 now acting as chromatic beamsplitter, and the optical elements returning beams of distinctwavenumbers to their respective emitters. Explicitly, the multi-spectralredirected beam 60 is incident on the beam combiner 46 at the same angle(e.g. relative to normal 46A), but will create different laser beamsexiting from the beam combiner 46 at different angles (which correspondto the angle of incidences 56A-56F), based on the respective wavenumbersin the redirected beam 60. Stated in another fashion, each laser beamreturning from the beam combiner 46 will be at a different return anglebased on wavenumber, these angles being, by wavenumber, the same as theincident angles. In turn, the wavenumber-distinct optical feedback toeach of the individual emitters creates the lowest-loss condition forthat emitter thereby driving the individual laser to resonate (“lase”)at that wavenumber. Thus, with the present design, each emitter incombination with the external optics comprises a laser lasing with acenter wavenumber dictated by geometry, and specifically dictated by theposition of the individual emitter within the array.

The system controller 24 controls the operation of the components of thelaser assembly 10. For example, the system controller 24 can include oneor more processors 24A, and one or more electronic storage devices 24B.In certain embodiments, the system controller 24 can control theelectron injection current to the individual emitters 18A-18F, andcontrol the thermal controller 34 to control the temperature of themounting base 30A.

In certain embodiments, the system controller 24 individually directscurrent to each of the emitters 18A-18G. For example, the systemcontroller 24 can continuously direct power to one or more of theemitters 18A-18G. Alternatively, for example, the system controller 24can direct power in a pulsed fashion to one or more of the emitters18A-18G. In one embodiment, the duty cycle is approximately fiftypercent. Alternatively, the duty cycle can be greater than or less thanfifty percent.

It should be noted that in the pulsed mode of operation, the systemcontroller 24 can simultaneous direct pulses of power to each of theemitters 18A-18G so that each of the emitters 18A-18G generates therespective beams 20A-20F at the same time. In this design, the assemblyoutput beam 12 is multi-spectral and made up the combined individuallaser beams 20A-20F.

Alternatively, the system controller 24 can direct pulses of power toone or more of the emitters 18A-18G at different times so that theemitters 18A-18G generate the respective beam 20A-20G at differenttimes. In this design, the characteristics of the assembly output beam12 can be controlled by which of the emitters 18A-18F are currentlyactivated. For example, in this design, each of the emitters 18A-18F canbe activated sequentially to generate an assembly output beam 12 havinga center wavenumber that changes over time. This design allows forindividually controllable emitter 18 (channels) for individualwavenumber generation for spectroscopy or other applications.Additionally, the lens mover 42D of the beam adjuster 42 can becontrolled to move one or both of the adjuster lenses 42A, 42B toselectively adjust the individual wavenumbers of the assembly outputbeam 12.

As provided herein, the system controller 24 can accept analog, digitalor software transmitted commands to pulse the assembly output beam 12with the desired pulse width and repetition rate. This feature allowsthe user to precisely adjust the characteristics of the assembly beam 12to meet the system requirements of the laser assembly 10.

The system controller 24 can utilize voltage or light-sensing circuitryto shut down in case of failure of one or more of the emitters 18, tobalance power, and/or to allow ‘digital’ spectroscopy whereby individualwavenumbers can be operated independently.

In certain embodiments, with the present designs, the beam combinersubassembly 22 is a high efficiency beam combiner. As alternative,non-exclusive examples, the beam combiner subassembly 22 can have acombination efficiency of at least 70, 75, 80, 85, 90, 95, 98, or 99percent. For example, if the combiner subassembly 22 has a combinationefficiency of eighty percent, this means that the output power of theassembly output beam 12 is eighty percent of the combined output powersof the emitters 18.

FIG. 1D is a simplified graph that illustrates a first set of differentcenter wavenumbers of the laser beams 20A-20F generated by the emitters18 (illustrated in FIG. 1A) when the beam adjuster 42 (illustrated inFIG. 1A) has a first demagnification (e.g. two times). In this example,the assembly output beam 12 (illustrated in FIG. 1A) will have a firstspectral width 62A.

FIG. 1E is a simplified graph that illustrates of the first set ofdifferent center wavenumbers versus angle of incidence. In thisembodiment, the laser beams collectively have a first range 63A ofangles of incidence.

Somewhat similarly, FIG. 1F is a simplified graph that illustrates asecond set of different center wavenumbers of the laser beams 20A-20Fgenerated by the emitters 18 (illustrated in FIG. 1A) when the beamadjuster 42 (illustrated in FIG. 1A) has a second demagnification (e.g.three times). In this example, the assembly output beam 12 (illustratedin FIG. 1A) will have a second spectral width 60B that is less than thefirst spectral width 62A of FIG. 1D.

FIG. 1G is a simplified graph that illustrates of the second set ofdifferent center wavenumbers versus angle of incidence. In thisembodiment, the laser beams collectively have a second range 63B ofangles of incidence that is less than the first range 63A illustrated inFIG. 1E.

Further, FIG. 1H is a simplified graph that illustrates a third set ofdifferent center wavenumbers of the laser beams 20A-20F generated by theemitters 18 (illustrated in FIG. 1A) when the beam adjuster 42(illustrated in FIG. 1A) has a third demagnification (e.g. four times).In this example, the assembly output beam 12 (illustrated in FIG. 1A)will have a third spectral width 62C that is less than the secondspectral width 62B of FIG. 1E.

FIG. 1I is a simplified graph that illustrates of the third set ofdifferent center wavenumbers versus angle of incidence. In thisembodiment, the laser beams collectively have a third range 63C ofangles of incidence that is less than the second range 63B illustratedin FIG. 1G.

FIG. 2 is a simplified top illustration of another embodiment of a laserassembly 210 that generates an assembly output beam 212. In thisembodiment, the laser assembly 210 includes a laser frame 214, an arrayof emitters 218, a lens array 232, a beam adjuster 242, a transform lensassembly 244, a beam combiner 246, and an output coupler 248 that aresimilar to the corresponding components described above and illustratedin FIG. 1A. However, in this embodiment, the laser assembly 210additionally includes a polarization rotator 266 (illustrated as a box)positioned between lens array 232 and the beam combiner 246. It shouldbe noted that the embodiment illustrated in FIG. 2 could be designedwithout the beam adjuster 242.

As provided above, each emitter 218 can be a Quantum Cascade emitter orother type of emitter that is bonded/mounted epi-side down. As a result,the laser beam 220 from each emitter 218 will have an electric field(polarization) having a first orientation 268 (into the page along the Zaxis, as illustrated by concentric circles in FIG. 2A) that isperpendicular (normal) to the emitter array axis 235A of the emitters218. However, if the wavelength selective beam combiner 246 is agrating, the beam combiner 246 will diffract laser beams with anelectric field having a second orientation 270 that is perpendicular tothe grating grooves (and parallel to the emitter array axis 235A) moreefficiently than laser beams having the first orientation 268 becausethe ridges 246A of the grating 246 will be oriented perpendicular to thesecond orientation of the laser beams. Stated in another fashion, thegrating 246 is more efficient for light having an E field polarizationthat is normal (perpendicular) to grooves 246A. The diffraction gratingshave higher diffraction efficiency and bandwidth when the incidentpolarization is perpendicular to the axis of grating grooves 246A.

Stated in yet another fashion, the laser beams 220 from each emitter 218will can have an s-polarization, and the polarization rotator 266 canrotate the laser beams at the beam combiner 246 to have ap-polarization.

In the embodiment illustrated in FIG. 2, the polarization rotator 266 isa ninety degrees rotator that rotates the first orientation 268 of thelaser beams 220 generated by the emitters 218 to the second orientation270 (illustrated as a two headed arrow) laser beams that are directed atthe beam combiner 246. Further, with this design, the output beam 212will have the second orientation 270, and the laser beams that propagatefrom the beam combiner 246 towards the emitters 218 are rotated back tothe first orientation 268 with the polarization rotator 266 prior toreturning to the emitters 218. This will improve the gain in each of theemitters 218, which can have a polarization dependent gain. For example,a Quantum Cascade emitter will have strong gains for a returning beamwith a polarization that is perpendicular to the gain layers.

In this embodiment, the polarization for laser beams 220 propagatingfrom the emitters 218 to the beam combiner 246 (from left to right inFIG. 2) are rotated ninety degrees by the polarization rotator 266 fromthe first orientation 268 to the second orientation 270. Further, thepolarization for laser beams 220 propagating from the beam combiner 246to the emitters 218 (from right to left in FIG. 2) are rotated ninetydegrees by the polarization rotator 266 from the second orientation 270to the first orientation 268.

In one embodiment, the polarization rotator 266 is wavelengthinsensitive to the spectral bandwidth of the assembly output beam 212.The polarization rotator 266 can be on axis or off axis and include oneor more waveplates. In one embodiment, the polarization rotator 266 caninclude a first rotator element (not shown) and a second rotator element(not show), and each rotator element rotates the polarization of thelight (E field polarization) by forty-five degrees. This embodimentresults in high efficiency for wide gain-bandwidth sources such asQuantum Cascade lasers. Other, non-exclusive examples of thepolarization rotator 266 can be (i) a one-half wave, non-dispersivepolarization rotator; (ii) a one-half wave Rhomb, dovetail, or otherprism polarization rotator that rotates the polarization of the inputbeam without rotating the image; (iii) a dispersion-compensated waveplate; (iv) an achromatic on-half wave plate; (iv) a thin filmpolarization rotating coating; (v) dispersive polarization rotator; (vi)a multi-order wave plate; or (vii) a zero order wave plate.

In one embodiment, the polarization rotator 266 rotates each beam ninetydegrees and has low dispersion. As provided herein, “low dispersion”shall mean that the polarization rotation angle does not substantiallychange with the emission wavelength. In one embodiment, low dispersionmeans that the polarization rotation angle for each of the beams islimited to 89-91 degree range across 3-12 um wavelength range. Inanother embodiment, low dispersion means that the polarization rotationvaries less than +/−ten degrees over the operating bandwidth of thelaser. In another example, if the polarization rotator 266 is designedto rotate all of the beams 90 degrees, all of the beams will have thepolarization rotated between 89 to 91 degrees. In this example, thewavelength range of the beams can be three to twelve microns.

It should be noted that in the embodiment illustrated in FIG. 2, thepolarization rotator 266 is positioned between the lens array 232 andthe beam adjuster 242. However, the polarization rotator 266 can bepositioned in another location between the lens array 232 and the beamcombiner 246.

For example, FIG. 3 is a simplified top illustration of yet anotherembodiment of a laser assembly 310 that includes a laser frame 314, anarray of emitters 318, a lens array 332, a beam adjuster 342, atransform lens assembly 344, a beam combiner 346, an output coupler 348,and a polarization rotator 366 that are similar to the correspondingcomponents described above and illustrated in FIG. 2. However, in thisembodiment, the polarization rotator 366 is positioned between the beamadjuster 342 and the transform lens assembly 344. It should be notedthat the embodiment illustrated in FIG. 3 could be designed without thebeam adjuster 342.

FIG. 4 is a simplified top illustration of still another embodiment of alaser assembly 410 that includes a laser frame 414, an array of emitters418, a lens array 432, a beam adjuster 442, a transform lens assembly444, a beam combiner 446, an output coupler 448, and a polarizationrotator 466 that are similar to the corresponding components describedabove and illustrated in FIG. 2. However, in this embodiment, thepolarization rotator 466 is positioned between the transform lensassembly 444 and the beam combiner 446. It should be noted that theembodiment illustrated in FIG. 4 could be designed without the beamadjuster 442.

FIG. 5 is a simplified top illustration of still another embodiment of alaser assembly 510 that includes (i) a laser frame 514, (ii) a lasersubassembly 516 that includes a laser mount 530, an array of emitters518 and a lens array 532, (iii) a beam adjuster 542, (iv) a transformlens assembly 544, (v) a beam combiner 546, (vi) an output coupler 548,and (vii) a polarization rotator 566 that are similar to thecorresponding components described above and illustrated in FIG. 1 or 2.However, in this embodiment, the laser assembly 510 also includes aspatial filter 572 that is positioned between the beam combiner 546 andthe output coupler 548.

It should be noted that the embodiment illustrated in FIG. 5 could bedesigned without the beam adjuster 542 and/or the polarization rotator566.

In FIG. 5, the spatial filter 572 reduces cross-talk by reducing lightthat is slightly off axis. Stated in another fashion, the spatial filter572 located between beam combiner 546 and output coupler 548 reduces andsuppresses optical crosstalk.

As provided herein, the desirable modes of the external cavity propagatebetween the high reflectivity coated facet of their respectiveindividual emitter 518 and the output coupler 548, in a manner that foreach mode the beam 558 is normal to the output coupler 548. The portionsof the beams transmitted thru the output coupler 548 travelconcentrically and colinearly to each other, forming the high qualityassembly output beam 512. The portions of the beams reflected off of theoutput coupler 548 return to their corresponding emitters 518, ratherthan neighboring emitters 518.

Crosstalk is a phenomenon when, for example, an external cavity of afirst emitter (including the grating and the output coupler) is lasingat one or more undesirable modes, a portion of the first beam from thefirst emitter will reflect off of the output coupler 548 at an anglewhich is not normal to the output coupler 548 and return to an adjacentemitter, e.g. a second emitter. The transmitted portion of the incidentbeams from cross talk modes will exit the cavity at different(non-normal) angles than the desirable modes, thus degrading the qualityof the assembly output beam 512.

As provided herein, the spatial filter 572 will suppress lasing at thecrosstalk external cavity modes by preferentially increasingintra-cavity losses of such modes.

The spatial filter 572 can have (i) diffraction limited transmission forthe combination beam 558; (ii) high losses for non-diffraction limitedcomponents of the combination beam 558; (iii) high transmission foroptical bandwidth of the combination beam 558 and optimized to minimizedispersion effects.

The design of the spatial filter 572 can be varied. In the non-exclusiveembodiment illustrated in FIG. 5, the spatial filter 572 includes afirst spatial lens 574, a second spatial lens 576 that is spaced apartfrom the first spatial lens 574, and a beam trimmer 578 positionedbetween the spatial lenses 574, 576. In this embodiment, the spatiallenses 574, 576 and the beam trimmer 578 are centered on the combinationaxis 558A. Further, (i) each spatial lens 574, 576 is operable in thewavenumbers of the assembly output beam 512; (ii) the first spatial lens574 focuses the combination beam 558 at a focal area 582; (iii) the beamtrimmer 578 can be a block that includes a transmission aperture 580(e.g. a pinhole or slit) that is position at the focal area 582; and(iv) the second spatial lens 576 can be a collimation lens.

FIG. 6 is a simplified top illustration of still another embodiment of alaser assembly 610 that generates an assembly output beam 612. In thisembodiment, the laser assembly 610 includes a laser frame 614, an arrayof emitters 618, a lens array 632, a beam adjuster 642, a transform lensassembly 644, a beam combiner 646, and an output coupler 648 that aresimilar to the corresponding components described above and illustratedin FIG. 1A. However, in this embodiment, the beam adjuster 642 ispositioned between the transform lens assembly 644 and the beam combiner646. With this design, the beam adjuster 642 reduces the range of anglesof incidences of at least some of the laser beams 620 on the beamcombiner 646 and reduces the resulting spectral width of the assemblyoutput beam 612. Stated in another fashion, the beam adjuster 642reduces at least some of angles of incidences of the laser beams 620 onthe beam combiner 646 as compared to a design without the beam adjuster642. It should be noted that in this embodiment, and the previouslydiscussed embodiments, an angle of incidence of the center beam may notbe affected by the beam adjuster 642, while the angle of incidence ofthe other beams will be adjusted by the beam adjuster 642.

It should also be noted that the spatial filter 572 of FIG. 5 can beimplemented in any of the laser assemblies 10, 210, 310, 410, 610disclosed herein. Further, a polarization rotator can be implemented ineach of these embodiments.

FIG. 7 is a simplified illustration of still another embodiment of alaser assembly 710. In this embodiment, the laser assembly 710 includes(i) a laser frame 714, (ii) a laser subassembly 716 having a pluralityof laser mounts 730, an array of emitters 718, and a lens array 732,(iii) a wavelength selective beam adjuster 742, (iv) a transform lensassembly 744, (v) a beam combiner 746, (vi) an output coupler 748, (vii)a polarization rotator 766, and (viii) a spatial filter 772 that aresimilar to the corresponding components described above and illustratedin FIG. 5.

However, in the embodiment illustrated in FIG. 7, the laser subassembly716 is divided into multiple, separate laser modules, e.g. a first lasermodule 716A, a second laser module 716B, and a third laser module 716Cthat are positioned so that the emitters 718A are aligned and spacedapart along the emitter array axis 735A. In FIG. 7, the lasersubassembly 716 is divided into three separate laser modules 716A-716C.Alternatively, laser subassembly 716 can be divided into more than threeor fewer than three laser modules 716A-716C.

In one embodiment, each laser module 716A-716C includes a separate lasermount 730, a separate set of one or more emitters 718A, and thecorresponding number of lenses 732A. In the simplified exampleillustrated in FIG. 7, each laser module 716A-716C includes a set of twoemitters 718A that are spaced apart along the emitter array axis 735Aand a set of two lenses 732A that are aligned along the lens array axis.As alternative, non-exclusive examples, each laser module 716A-716C caninclude a set of at least 1, 2, 3, 4, 5, 7, 8, 9, 10, 15, 20, 25, or 30separate emitters 718A that are tightly arranged along the linearemitter array 735A, and the corresponding number of lenses 732A.

For example, the division of the laser subassembly 716 into multipledifferent modules 716A, 716B, 716C can make the laser subassembly 716easier to manufacture and/or can provide more accurate thermal controlwith the thermal controller 734. For example, because the emitters 718Aon the first laser module 716A will lase at different center wavenumbersthan the emitters 718A on the third laser module 716C, it may benecessary to have the emitters 718A on the first laser module 716A bedifferent from the emitters 718A on the third module 716C. Thus, it maybe easier to make them differently if they are part of different modules716A, 716C. Further, the cooling requirements for the emitters 718A maybe different for each of the laser modules 716A-716C. Thus, accuratelycontrolling the temperature of the emitters 718A can be simplified byindividually cooling the laser modules 716A-716C with the thermalcontroller 734.

It should be noted that the embodiment illustrated in FIG. 7 could bedesigned without the beam adjuster 742, the spatial filter 772, and/orthe polarization rotator 766.

It should be noted that (i) the emitters 718A on the first laser module716A can be referred to as first emitters; (ii) the emitters 718A on thesecond laser module 716B can be referred to as second emitters; and(iii) the emitters 718A on the third laser module 716C can be referredto as third emitters. Further, the first emitters are spaced apart fromthe second emitters along the emitter array axis 735A, and the secondemitters are spaced apart from the third emitters along the emitterarray axis 735A.

FIG. 8A is a simplified illustration of another embodiment of a laserassembly 810 that includes (i) a laser frame 814, (ii) a lasersubassembly 816 that includes a plurality of laser mount 830, an arrayof emitters 818 and a lens array 832, (iii) a wavelength selective beamadjuster 842, (iv) a transform lens assembly 844, (v) a beam combiner846, (vi) an output coupler 848, (vii) a polarization rotator 866, and(viii) a spatial filter 872 that are similar to the correspondingcomponents described above and illustrated in FIG. 7. Further, anassembly output beam 812 will be multispectral because each of theindividual emitters 818A is lasing at a different center wavenumber as aresult of the arrangement of the laser assembly 810.

However, in the embodiment illustrated in FIG. 8A, the laser subassembly816 is divided into multiple, separate laser modules, e.g. a first lasermodule 816A, and a second laser module 816B that are positioned so thatthe emitters 818A are aligned and spaced apart along the emitter arrayaxis 835A. In FIG. 8A, the laser subassembly 816 is divided into twoseparate laser modules 816A, 816B. Alternatively, laser subassembly 816can be divided into more than two laser modules 816A, 816B.

In this embodiment, each laser module 816A, 816B includes a separatelaser mount 830, a separate set of emitters 818A, and a correspondingset of lenses 832A. In the simplified example illustrated in FIG. 8A,each laser module 816A, 816B includes a set of three emitters 818A thatare spaced apart along the emitter array axis 835A and a set of threelenses 832A that are aligned along the lens array axis. As alternative,non-exclusive examples, each laser module 816A, 816B can include atleast 1, 2, 3, 4, 5, 7, 8, 9, 10, 15, 20, 25, or 30 separate emitters818A that are tightly arranged in the linear emitter array 835A, and thecorresponding number of lenses 832A. It should be noted that theemitters 818A for the first laser module 816A can be referred to as afirst set of emitters 819A or first emitters, and the emitters 818A forthe second laser module 816B can be referred to as a second set ofemitters 819B of second emitters.

In certain embodiments, (i) the laser modules 816A, 816B are spacedapart, and (ii) the first set of emitters 819A of the first laser module816A are spaced apart an emitter separation distance 890 along theemitter array axis 835A from the second set of emitters 819B of thesecond laser module 816B. In alternative, non-exclusive embodiments, theemitter separation distance 890 is at least 0.1, 0.5, 1, 5, 10, 50, or100 millimeters.

With the design illustrated in FIG. 8A, each emitters 818A will lase ata different center wavenumber. In FIG. 8A, each of the emitters 818A ofthe first set of emitters 819A will generate a laser beam 820 having adifferent center wavenumber that is within a relative small firstspectral range (“first color range”) because the emitters 818A of thefirst laser module 816A are physically relatively close together.Similarly, each of the emitters 818A of the second set of emitters 819Bwill generate a laser beam 820 having a different center wavenumber thatis within a relative small second spectral range (“second color range”)because the emitters 818A of the second laser module 816B are physicallyrelatively close together.

Further, there will be a spectral gap between the first spectral rangeand the second spectral range, and the size of that spectral gap willdepend on the size of the emitter separation distance 890. Generallyspeaking, this spectral gap will increase as the emitter separationdistance 890 is increased, and this spectral gap will decrease as theemitter separation distance 890 is decreased.

As alternative, non-exclusive examples, (i) the first spectral range canbe less than 0.025, 0.05, 0.1, 0.2, 0.3, 0.5, 0.75, 1, 1.5, or 3microns; (ii) the second spectral range can be less than 0.025, 0.05,0.1, 0.2, 0.3, 0.5, 0.75, 1, 1.5, or 3 microns; and (iii) the spectralgap can be greater than 0.1, 0.5, 1, 2, 5, or 10 microns.

With the present design, (i) the wavenumbers in the first spectralrange; (ii) the wavenumbers in the second spectral range; and (iii) thesize of the spectral gap can be adjusted by adjusting the position ofeach laser module 816A, 816B relative to the other components.

In one nonexclusive embodiment, (i) the first laser module 816A caninclude a first stage 892A that retains the laser mount 830 of the firstlaser module 816A, and a first mover 892B that can selectively move thefirst stage 892A and the laser mount 830 of the first laser module 816Ato selectively adjust the location of the first set of emitters 819Aalong the emitter array axis 835A; and/or (ii) the second laser module816B can include a second stage 894A that retains the laser mount 830 ofthe second laser module 816B, and a second mover 894B that canselectively move the second stage 894A and the laser mount 830 of thesecond laser module 816B to selectively adjust the location of thesecond set of emitters 819B along the emitter array axis 835A.

With this design, (i) the first mover 892B can be controlled to positionthe first set of emitters 819A to achieve the desired wavenumbers in thefirst spectral range; and (ii) the second mover 894B can be controlledto position the second set of emitters 819B to achieve the desiredwavenumbers in the second spectral range. With this design, the movers892B, 894B can be controlled to account for transform lens dispersioneffects.

It should be noted that one or both movers 892B, 894B can be an actuatorsuch as a linear actuator. Alternatively, one or both movers 892B, 894Bcan be a manual type of mover. Still alternatively, one or both lasermodules 816A, 816B can be individually positioned without the respectivestage and/or mover.

As provided herein, the division of the laser subassembly 816 intomultiple different modules 816A, 816B can make the laser subassembly 816easier to manufacture, can allow for adjustment of the spectral ranges,and/or can provide more accurate thermal control with the thermalcontroller 834.

It should be noted that the embodiment illustrated in FIG. 8A could bedesigned without the beam adjuster 842, the spatial filter 872, and/orthe polarization rotator 866. It should also be noted that the lasersubassembly 816 can be designed to include three or more laser modules816A, 816B that are spaced apart along the emitter array axis 835A.

FIG. 8B is a simplified graph that illustrates (i) the different centerwavenumbers 820A-820C of the laser beams generated by the first set ofemitters 819A (illustrated in FIG. 8A) of the laser assembly 810 of FIG.8A span a first spectral range 895B; (ii) the different centerwavenumbers 820D-820F of the laser beams generated by the second set ofemitters 819B (illustrated in FIG. 8A) of the laser assembly 810 of FIG.8A span a second spectral range 896B; and (iii) the size of the spectralgap 897B that separates the spectral ranges 895B, 896B.

With reference to FIGS. 8A and 8B, each of the emitters 818A of thefirst set of emitters 819A will have a different center wavenumber thatis within the relative small first spectral range 895B because theemitters 818A of the first laser module 816A are relatively closetogether. Similarly, each of the emitters 818A of the second set ofemitters 819B will have a different center wavenumber that is within therelative small second spectral range 896B because the emitters 818A ofthe second laser module 816B are relatively close together.

Further, as provided above, (i) the wavenumbers in the first spectralrange 895B; (ii) the wavenumbers in the second spectral range 896B; and(iii) the size of the spectral gap 897B can be adjusted by adjusting theposition of each laser module 816A, 816B relative to the othercomponents.

FIG. 8C is a simplified graph that illustrates another set ofwavenumbers that can be generated by the laser assembly 810 of FIG. 8Awhen both laser modules 816A, 816B are moved (not shown) to reduce theemitter separation distance 890. With reference to FIGS. 8A and 8C, (i)the different center wavenumbers 820A-820C of the laser beams generatedby the first set of emitters 819A (illustrated in FIG. 8A) of the laserassembly 810 span the first spectral range 895C; (ii) the differentcenter wavenumbers 820D-820F of the laser beams generated by the secondset of emitters 819B (illustrated in FIG. 8A) of the laser assembly 810of FIG. 8A span the second spectral range 896C; and (iii) the size ofthe spectral gap 897C has been reduced.

FIG. 9 is a simplified illustration of still another embodiment of alaser assembly 910 that includes (i) a laser frame 914, (ii) a lasersubassembly 916 having a plurality of laser mounts 930, an array ofemitters 918 and a lens array 932, (iii) a transform lens assembly 944,(iv) a wavelength selective beam combiner 946, (v) an output coupler948, (vi) a polarization rotator 966, and (vii) a spatial filter 972that are similar to the corresponding components described above andillustrated in FIG. 8A.

In FIG. 9, the laser subassembly 916 includes a first laser module 916A,and a second laser module 916B that are spaced apart an emitterseparation distance 990 along an emitter array axis 935A. The lasermodules 916A, 9168 can be similar to the corresponding componentsdescribed above and illustrated in FIG. 8A. However, the laser assembly910 of FIG. 9 does not include a beam adjuster 842 (illustrated in FIG.8A). As a result thereof, the laser subassembly 916 will utilize feweremitters 918 for a given form factor, and the spectral width of theassembly output beam 912 may be greater than the embodiment illustratedin FIG. 8A. Further, a larger transform lens assembly 944 may benecessary to direct the beams 920 at the beam combiner 946.

It should be noted that the embodiment illustrated in FIG. 9 could bedesigned without the spatial filter 972, and/or the polarization rotator966. It should also be noted that the laser subassembly 916 can bedesigned to include three or more laser modules 916A, 916B that arespaced apart along the emitter array axis 935A.

FIG. 10 is a simplified illustration of another embodiment of apolarization rotator 1066 that can be used in the laser assemblies 10,210, 310, 410, 510, 610, 710, 810, 910 described above to rotate eachlaser beam 1020 (only one is illustrated) ninety degrees and has lowdispersion. In this embodiment, the polarization rotator 1066 is arhombohedral half wave plate. In this design, there are two internalreflections, with each reflection rotating the polarization by 45degrees. Further, the half wave plate rhombohedral can include opticalcoatings to reduce reflective losses.

FIG. 11 is a simplified illustration of another embodiment of awavelength selective beam adjuster 1142 having features of the presentinvention. In this embodiment, the beam adjuster 1142 again compressesthe spacing between the laser beams 1120 to provide the adjusted laserbeams 1150, and adjusts the spectral width of the assembly output beam(not shown in FIG. 11). Depending upon the direction in which the laserbeams are propagating, the beam adjuster 1142 can spatially demagnify orspatially magnify the laser beams. In FIG. 11, for the laser beams 1120propagating left to right, the beam adjuster 1142 demagnifies the beamarray by first converging and subsequently collimating the laser beams1120 to provide the array of adjusted laser beams 1150 that are moretightly packed. Alternatively, for laser beams propagating from right toleft in FIG. 11, the beam adjuster 1142 magnifies the beam array byfirst diverging and subsequently collimating the laser beams. With thisdesign, the beam adjuster 1142 expands the spacing between the laserbeams moving right to left so that the laser beams are properly spacedto be directed back to the respective emitters (not shown in FIG. 12).

With reference to FIG. 11, the beam adjuster 1142 is somewhat similar toa Galilean telescope and includes a first adjuster lens 1142A (bi-convexobjective lens) and a second adjuster lens 1142B (bi-concave ocular)that are spaced apart.

FIG. 12 is a simplified illustration of another embodiment of a laserassembly 1210 that generates an assembly output beam 1212. In thisembodiment, the laser assembly 1210 includes (i) a laser frame 1214,(ii) a laser subassembly 1216 that includes a plurality of laser mounts1230, an array of emitters 1218 and a lens array 1232, (iii) awavelength selective beam adjuster 1242, (iv) a transform lens assembly1244, (v) a beam combiner 1246, (vi) an output coupler 1248, (vii) apolarization rotator 1266, and (viii) a spatial filter 1272 that aresimilar to the corresponding components described above and illustratedin FIG. 8A. Further, an assembly output beam 1212 will be multispectralbecause each of the individual emitters 1218A is lasing at a differentcenter wavenumber as a result of the arrangement of the laser assembly1210. However, in the embodiment illustrated in FIG. 12, the laserassembly 1210 also includes one or more path length adjusters 1299 (onlyone is illustrated in FIG. 12).

Similar to FIG. 8A, the laser subassembly 1216 of FIG. 12 is dividedinto multiple, separate laser modules, e.g. a first laser module 1216A,and a second laser module 1216B that are positioned so that the emitters1218A are aligned and spaced apart along the emitter array axis 1235A.In FIG. 12, the laser subassembly 1216 is divided into two separatelaser modules 1216A, 1216B. Alternatively, the laser subassembly 1216can be divided into more than two laser modules 1216A, 1216B.

In this embodiment, each laser module 1216A, 1216B includes a separatelaser mount 1230, a separate set of emitters 1218A, and a correspondingset of lenses 1232A. In the simplified example illustrated in FIG. 12,each laser module 1216A, 1216B includes a set of three emitters 1218Athat are spaced apart along the emitter array axis 1235A and a set ofthree lenses 1232A that are aligned along the lens array axis. Asalternative, non-exclusive examples, each laser module 1216A, 1216B caninclude at least 1, 2, 3, 4, 5, 7, 8, 9, 10, 15, 20, 25, or 30 separateemitters 1218A that are tightly arranged along the linear emitter axis1235A, and the corresponding number of lenses 1232A. It should be notedthat the emitters 1218A for the first laser module 1216A can be referredto as a first set of emitters 1219A or first emitters, and the emitters1218A for the second laser module 1216B can be referred to as a secondset of emitters 1219B of second emitters.

In certain embodiments, (i) the laser modules 1216A, 1216B are spacedapart, and (ii) the first set of emitters 1219A of the first lasermodule 1216A are spaced apart an emitter separation distance 1290 alongthe emitter array axis 1235A from the second set of emitters 1219B ofthe second laser module 1216B. In alternative, non-exclusiveembodiments, the emitter separation distance 1290 is at least 0.1, 0.5,1, 5, 10, 50, or 100 millimeters.

With the design illustrated in FIG. 12, each emitters 1218A will lase ata different center wavenumber. In FIG. 12, each of the emitters 1218A ofthe first set of emitters 1219A will generate a separate first laserbeam 1220A having a different center wavenumber that is within arelative small first spectral range (“first color range”) because theemitters 1218A of the first laser module 1216A are physically relativelyclose together. Similarly, each of the emitters 1218A of the second setof emitters 1219B will generate a separate second laser beam 1220Bhaving a different center wavenumber that is within a relative smallsecond spectral range (“second color range”) because the emitters 1218Aof the second laser module 1216B are physically relatively closetogether.

Further, in this embodiment, there will be a spectral gap between thefirst spectral range and the second spectral range, and the size of thatspectral gap will depend on the size of the emitter separation distance1290. Generally speaking, this spectral gap will increase as the emitterseparation distance 1290 is increased, and this spectral gap willdecrease as the emitter separation distance 1290 is decreased. The pathlength adjuster 1299 can be used to change the divergence.

As provided herein, the path length adjuster 1299 allows for arelatively large spectral gap while being maintaining near diffractionlimited collimation of the two beam sets 1220A, 1220B. The path lengthadjuster 1299 can be used to adjust the focal length of the transformlens assembly 1244. With this design, for example, the laser assembly1210 can be used to generate an output beam 1212 that includesmid-wavelength MIR light (e.g. three to five microns) andlong-wavelength MIR light (e.g. eight to twelve microns) from the samelaser cavity and pointing in the same direction. As alternative,non-exclusive examples, the spectral gap can be greater than 0.001, 0.1,0.5, 1, 2, 5, or 10 microns.

As provided herein, one or more path length adjusters 1299 can bepositioned to adjust the path length of the first laser beams 1220Aand/or the second laser beams 1220B. In FIG. 12, a single path lengthadjuster 1299 is used for the first laser beams 1220A. Alternatively oradditionally, a path length adjuster (not shown) can be used to adjustthe path length of the second laser beams 1220B.

The design of the path length adjuster 1299 can be varied. In oneembodiment, the path length adjuster 1299 includes an optical element(e.g. a window or glass) that is positioned in the path of the firstlaser beams 1220A. The optical element can be operable in the range ofthe first laser beams 1220A and be coated with anti-reflective coatings.

With this design, the path length of the first laser beams 1220A can beadjusted by adjusting the rotational position of the path lengthadjuster 1299 to compensate for the path length of the first laser beams1220A between the first laser module 1216A and the transform lensassembly 1244. Generally speaking, more rotation results in increasingthe path length of the first laser beams 1220A, and decreasing rotationresults in decreasing the path length of the first laser beams 1220A.With this design, the path length adjuster 1299 can be selectivelyrotated so that the transform lens assembly 1244 collimates and directsthe laser beams 1220A, 1220B to spatially overlap at the focal plane.

In one embodiment, after the rotational position of the path lengthadjuster 1299 is properly set, the path length adjuster 1299 can befixed, e.g. to the laser frame 1214. For example, the optical element1299 can glued or fixedly secured in another fashion. In otherembodiment, the rotational position can be adjusted on demand using anactuator.

Alternatively, or additionally, the path length adjuster 1299 caninclude a separate optical element (not shown) positioned in the path ofthe second laser beams 1220B.

As provided herein, the path length adjuster 1299 can be positionedbetween the first set of emitters 1219A and the transform lens assembly1244. In FIG. 12, the path length adjuster 1299 is positioned betweenthe first set of emitters 1219A and the beam adjuster 1242. However, thepath length adjuster 1299 could be alternatively located.

Additionally, and optionally, in one nonexclusive embodiment, (i) thefirst laser module 1216A can include a first stage 1292A that retainsthe laser mount 1230 of the first laser module 1216A, and a first mover1292B that can selectively move the first stage 1292A and the lasermount 1230 of the first laser module 1216A to selectively adjust thelocation of the first set of emitters 1219A along the emitter array axis1235A; and/or (ii) the second laser module 1216B can include a secondstage 1294A that retains the laser mount 1230 of the second laser module1216B, and a second mover 12948 that can selectively move the secondstage 1294A and the laser mount 1230 of the second laser module 1216B toselectively adjust the location of the second set of emitters 12198along the emitter array axis 1235A.

With this design, (i) the first mover 1292B can be controlled toposition the first set of emitters 1219A to achieve the desiredwavenumbers in the first spectral range; and (ii) the second mover 1294Bcan be controlled to position the second set of emitters 1219B toachieve the desired wavenumbers in the second spectral range. With thisdesign, the movers 12928, 12948 can be controlled to account fortransform lens dispersion effects.

It should be noted that, for example, the embodiment illustrated in FIG.12 could be designed without the beam adjuster 1242, the spatial filter1272, and/or the polarization rotator 1266. It should also be noted thatthe laser subassembly 1216 can be designed to include three or morelaser modules 1216A, 1216B that are spaced apart along the emitter arrayaxis 1235A. For example, the laser assembly 1210 can include a separatepath length adjuster 1299 for one or more of the laser modules 1216A,1216B.

FIG. 13 is a simplified illustration of another embodiment of a laserassembly 1310 that generates an assembly output beam 1312. In thisembodiment, the laser assembly 1310 includes (i) a laser frame 1314,(ii) a laser subassembly 1316 with a first laser module 1316A and asecond laser module 1316B, (iii) a wavelength selective beam adjuster1342, (iv) a transform lens assembly 1344, (v) a beam combiner 1346,(vi) an output coupler 1348, (vii) a polarization rotator 1366, and(viii) a spatial filter 1372 that are similar to the correspondingcomponents described above and illustrated in FIG. 12. However, in theembodiment illustrated in FIG. 13, the path length adjuster 1399positioned in the path of the first laser beams 1320A is located betweenthe beam adjuster 1342 and the transform lens assembly 1344. In thisembodiment, the path length adjuster 1399 again allows for a relativelylarge spectral gap for the output beam 1312.

FIG. 14A is a simplified illustration of another embodiment of a laserassembly 1410 that generates an assembly output beam 1412. In thisembodiment, the laser assembly 1410 includes (i) a laser frame 1414,(ii) a laser subassembly 1416 with a first laser module 1416A and asecond laser module 1416B, (iii) a beam adjuster 1442, (iv) a transformlens assembly 1444, (v) a beam combiner 1446, (vi) an output coupler1448, (vii) a polarization rotator 1466, and (viii) a spatial filter1472 that are similar to the corresponding components described aboveand illustrated in FIG. 12. However, in the embodiment illustrated inFIG. 14, instead of using a path length adjuster 1299 (illustrated inFIG. 12), the transform lens assembly 1444 is uniquely designed toprovide a first focal length for the first laser beams 1420A and asecond focal length for the second laser beams 1420B so that thetransform lens assembly 1440 directs the laser beams 1420A, 1420B tospatially overlap at a focal plane of the transform lens assembly 1444.In this embodiment, the first focal length is different from the secondfocal length.

FIG. 14B is a simplified illustration of a first embodiment of thetransform lens assembly 1444. In this example, the transform lensassembly 1444 is a multiple segment lens that includes a first segment1444A and a second segment 1444B that are positioned adjacent eachother. In this embodiment, the first segment 1444A is designed to have afirst focal length, and the second segment 1444B is designed to have asecond focal length that is different from the first focal length. Inone embodiment, the first segment 1444A can be cut from a first lens(not shown) and the second segment 1444B can be cut from a second lens(not shown). Subsequently, the segments 1444A, 1444B can be joinedtogether to form the transform lens assembly 1444.

FIG. 14C is a simplified illustration of yet another embodiment of thetransform lens assembly 1444C. In this example, the transform lensassembly 1444C includes a first lenses 1444D that defines the firstsegment 1444A having the first focal length, and a second lenses 1444Ethat defines the second segment 1444B having the second focal length. Inthis embodiment, the lenses 1444D, 1444E are positioned adjacent eachother and are aligned along a lens axis 1444F.

FIG. 15A is a simplified, perspective illustration of a portion of alaser subassembly 1516 including an emitter array 1517 and a laser mount1530. In this non-exclusive embodiment, the emitter array 1517 includesan emitter body 1517A, a plurality of spaced apart emitters 1518embedded in the emitter body 1517A, and a plurality of spaced apartinsulators 1517B. In this embodiment, the laser mount 1530 is uniquelydesigned, and the emitter array 1517 is secured to the laser mount 1530in a unique fashion to inhibit shorting of the emitter array 1517. FIG.15B is a front view of a portion of FIG. 15A.

With reference to FIGS. 15A and 15B, the emitter body 1517A can begenerally rectangular shaped and can include an emitter top 1517C, andemitter bottom 1517D, a pair of emitter sides 1517E, an emitter front1517F, and an emitter rear (not shown in the Figures). In oneembodiment, the emitter bottom 1517D includes a plurality of extensions1517G. In this design, each emitter 1518 is positioned in a separateextension 1517G and the extensions 1517G are secured directly to thelaser mount 1530. For example, each extension 1517G can be soldered tothe laser mount 1530 using an indium solder.

In one embodiment, the emitter body 1518A includes the plurality ofspaced apart emitters 1518 that cooperate to emit at least a portion ofthe assembly output beam. In this embodiment, the emitters 1518 arespaced apart along an emitter array 1518A and the emitters 1518 arepositioned near the emitter bottom 1517D. Further, the emitter body1518A includes the plurality of insulators 1517B that are also spacedapart along the emitter array 1518A. With this design, an insulator1517B is positioned between each adjacent emitter 1518. In oneembodiment, each emitter 1518 is a QC gain medium.

The number, size, shape and design of the emitters 1518 can be varied toachieve the desired characteristics of the assembly output beam. Forexample, the emitter array 1517 can include between two and twentyemitters 1518. In certain embodiments, the emitters 1518 can bebonded/mounted epi-side down to the laser mount 1530.

The emitter body 1517A is mounted to and electrically connected to thelaser mount 1530. The design of the laser mount 1530 can be varied. InFIGS. 15A and 15B, the laser mount 1530 is generally rectangular shapedand includes a mount top 1530A, a mount bottom 1530B, a pair of mountsides 1530C, a mount front 1530D, and a mount rear (not shown).

In this embodiment, the mount top 1530A defines a generally flatmounting region 1531A, a first gap region 1531B, and a second gap region1531C that is spaced apart from the first gap region 1531B. With thisdesign, the emitter body 1517A is directly secured to the mountingregion 1531A and cantilevers over the first gap region 1531B and thesecond gap region 1531C. The design of each gap region 1531B, 1531C canbe varied. In this embodiment, each gap region 1531B, 1531C is arectangular shaped trench (slot) in the mount top 1530A. Alternatively,one or both gap regions 1531B, 1531D can have another configuration.These gap regions 1531B, 1531C provide an area for the emitter body1517A to overhang.

The gap regions 1531B, 1531C provides a gap 1531 between the emitterbottom 1517D and the laser mount 1530 near the respective emitter side1517E. In alternative, non-exclusive embodiments, the gap 1531 is atleast approximately 0.01, 0.05, 0.1, 0.2, 0.5, or 1 millimeter.

The laser mount 1530 can be made of rigid material that has a relativelyhigh thermal conductivity to act as a conductive heat spreader. Incertain embodiments, the material used for the laser mount 1530 can beselected so that its coefficient of thermal expansion matches thecoefficient of thermal expansion of the emitters 1518.

In one embodiment, the controller 24 (illustrated in FIG. 1) iselectrically connected to the emitter top 1517C to provide current tothe emitter array 1517. Further, the emitter bottom 1517D is soldered tothe laser mount 1530 near each emitter 1518 to provide the return pathof the current via the laser mount 1530. With this design, theinsulators 1517B separate the respective emitters 1518, and the currentflows from the emitter top 1517C through each emitter 1518 to the lasermount 1530 to generate the beams.

As provided herein, in the event solder flows up the emitter side 1517Eover the end insulator 1517B, the solder can short to the laser mount1530, thereby causing current to not flow through each emitter 1518. Asprovided herein, because the emitter body 1517A extends over the gapregions 1531B, 1531C, any solder will have to traverse a relatively longpath to short out the emitter array 1517. Thus, it is less likely toshort out the emitter array.

FIG. 16A is a simplified, perspective illustration of a portion ofanother laser subassembly 1616 including an emitter array 1617 and alaser mount 1630 that are somewhat similar to the correspondingcomponents described above and illustrated in FIGS. 15A and 15B. In thisnon-exclusive embodiment, the emitter array 1617 includes the emitterbody 1617A, the plurality of spaced apart emitters 1618, and theplurality of spaced apart insulators 1617B. FIG. 16B is a front view ofa portion of FIG. 16A.

With reference to FIGS. 16A and 16B, in this embodiment, the emitterbody 1617A is directly secured to the mounting region 1631A, and theemitter body 1617A again cantilevers over the first gap region 1631B andthe second gap region 1631C. However, in this embodiment, more of theemitter body 1617A cantilevers over the respective gap region 1631B,1631C. More specifically, in this embodiment, at least one emitter 1618on each side of the emitter body 1617A extends over the gap regions1631B, 1631C. Stated in another fashion, in this embodiment, a leftmostemitter 1618 cantilevers over the first gap region 1631B, and arightmost emitter 1618 cantilevers over the second gap region 1631B. Itshould be noted that with this design, the leftmost and rightmostemitters 1618 will not be active because current will not flow throughthese emitters 1618.

In this embodiment, the controller 24 (illustrated in FIG. 1) again iselectrically connected to the emitter top 1617C to provide current tothe emitter array 1617. Further, the emitter bottom 1617D is soldered tothe laser mount 1630 near each emitter 1618 (except for the twooverhanging side emitters 1618) to provide the return path of thecurrent via the laser mount 1630. With this design, the insulators 1617Bseparate the respective emitters 1618, and the current flows from theemitter top 1617C through each emitter 1618 (except for the twooverhanging side emitters 1618) to the laser mount 1630 to generate thebeams.

As provided herein, because the emitter body 1617A extends over the gapregions 1631B, 1631C, any solder will have to traverse a relatively longpath to short out the emitter array 1617. Thus, it is less likely toshort out the emitter array 1617.

It should also be noted that the laser assemblies 10, 210, 310, 410,510, 610, 710, 810, 910 provided herein can be used in many differentapplications, including, but not limited to, spectroscopy, chemicaldetection, medical diagnostics, pollution monitoring, leak detection,analytical instruments, homeland security, remote chemical sensing,industrial process control.

For example, if the laser assemblies 10, 210, 310, 410, 510, 610, 710,810, 910 are used for spectroscopy, (i) the system can be designed sothat wavenumbers of the assembly output beam coincide with absorptionpeaks of materials being detected; (ii) the system can be designed sothat wavenumbers of the assembly output beam coincide withtransparencies of the materials being detected for purposes ofbaselining system performance; (iii) the system can have individuallycontrollable emitters for single or multiple co-propagating wavelengthswith individual control.

Still alternatively, for example, the laser assemblies 10, 210, 310,410, 510, 610 can be used on an aircraft (e.g. a plane or helicopter) aspart of a jammer system of an anti-aircraft missile.

In yet another design, at least a portion of the refractive optics canbe replaced with reflective optics for the laser assemblies 10, 210,310, 410, 510, 610,

While the particular designs as shown and disclosed herein is fullycapable of obtaining the objects and providing the advantages hereinbefore stated, it is to be understood that it is merely illustrative ofthe presently preferred embodiments of the invention and that nolimitations are intended to the details of construction or design hereinshown other than as described in the appended claims.

What is claimed is:
 1. A laser assembly that generates an assemblyoutput beam, the laser assembly comprising: a laser subassemblyincluding a first laser module that emits a plurality of spaced apart,substantially parallel first laser beams, and a second laser module thatemits a plurality of spaced apart, substantially parallel second laserbeams; a transform lens assembly positioned in a path of the laserbeams, the transform lens assembly collimating the laser beams anddirecting the laser beams to spatially overlap at a focal plane of thetransform lens; a wavelength selective beam combiner positioned at thefocal plane that combines the lasers beams to provide a combination beamthat is directed along a combination axis; and a path length adjusterpositioned in a path of the first laser beams, the path length adjusterbeing adjustable to adjust of a path length the first laser beamsrelative to the second laser beams.
 2. The laser assembly of claim 1wherein the first laser module is spaced apart from the second lasermodule an emitter separation distance along an emitter array axis. 3.The laser assembly of claim 2 wherein the emitter separation distance isat least 0.5 millimeters.
 4. The laser assembly of claim 1 furthercomprising a polarization rotator, wherein the laser beams from thelaser subassembly have a first polarization orientation, and thepolarization rotator rotates the polarization so that the laser beamsdirected at the beam combiner will have a second polarizationorientation that is ninety degrees different from the first polarizationorientation.
 5. The laser assembly of claim 1 further comprising a beamadjuster positioned in a path of the laser beams, the beam adjusteradjusting the spacing between the plurality of laser beams.
 6. The laserassembly of claim 5 wherein the path length adjuster is positionedbetween the first laser module and the beam adjuster.
 7. The laserassembly of claim 5 wherein the path length adjuster is positionedbetween the beam adjuster and the beam combiner.
 8. The laser assemblyof claim 1 wherein the path length adjuster is positioned between thefirst laser module and the transform lens assembly.
 9. The laserassembly of claim 1 wherein the first laser module includes firstemitters and the second laser module includes second emitters, andwherein the first emitters and the second emitters are aligned along anemitter array axis.
 10. The laser assembly of claim 1 further comprisingan output coupler positioned on the combination axis that redirects atleast a portion of the combination beam back to the beam combiner as aredirected beam, and transmits a portion of the combination beam as theassembly output beam.
 11. The laser assembly of claim 10 furthercomprising a spatial filter positioned between the beam combiner and theoutput coupler that suppresses cross-talk.
 12. A laser assembly thatgenerates an assembly output beam, the laser assembly comprising: alaser subassembly including a first laser module that emits a pluralityof spaced apart, substantially parallel first laser beams, and a secondlaser module that emits a plurality of spaced apart, substantiallyparallel second laser beams; a transform lens positioned in a path ofthe laser beams, the transform lens assembly collimating the laser beamsand directing the laser beams to spatially overlap at a focal plane ofthe transform lens; and a wavelength selective beam combiner positionedat the focal plane that combines the lasers beams to provide acombination beam that is directed along a combination axis; wherein thetransform lens includes a first lens segment having a first focal lengthand a second lens segment having a second focal length that is differentfrom the first focal length, wherein the first lens segment directs thefirst laser beams at the focal plane and the second lens segment directsthe second laser beams at the focal plane.
 13. The laser assembly ofclaim 12 wherein the first lens segment and the second lens segment aresecured together.
 14. The laser assembly of claim 12 wherein the firstlens segment and the second lens segment are aligned along a lens axis.15. The laser assembly of claim 12 wherein the first laser module isspaced apart from the second laser module an emitter separation distancealong an emitter array axis, wherein the emitter separation distance isat least 0.5 millimeters.
 16. The laser assembly of claim 12 furthercomprising a beam adjuster positioned in a path of the laser beams, thebeam adjuster adjusting the spacing between the plurality of laserbeams.
 17. A laser assembly that generates an assembly output beam, thelaser assembly comprising: an emitter body that includes a plurality ofspaced apart emitters that cooperate to emit at least a portion of theassembly output beam; a controller that directs current to the emitterbody; and a laser mount that is electrically connected the emitter body,the laser mount includes a mounting region and a first gap region;wherein the emitter body is coupled to the laser mount with at least aportion of emitter body cantilevering over the first gap region.
 18. Thelaser assembly of claim 17 wherein the laser mount includes a second gapregion that is spaced apart from the first gap region, and wherein theemitter body cantilevers over both the first gap region and the secondgap region.
 19. The laser assembly of claim 18 wherein at least oneemitter is positioned over the first gap region and wherein at least oneemitter is positioned over the second gap region.
 20. The laser assemblyof claim 17 wherein at least one emitter is positioned over the firstgap region.